Either way, here's a list of my recommendations, from most to least preferred. I didn't really account for price because I don't know where you're going to be buying them or what you consider a limited budget:
- Marineland C-360 ($168.99) or Rena Filstar XP3 ($184.99)
I have the C-360 and I'm very happy with it. I've heard they have bypass issues and I just did some experimentation with my C-220 that would seem to confirm what I've heard, but bypass issues or not they seem to work OK. I have not used the Filstar, but the guy that manages my LFS recommends it over the Marineland even though he doesn't carry it. He knows his stuff and I'd be inclined to take him at his word on this one. I'll probably pick up an XP3 for my 29G when I set it up.
- Eheim 2217 ($158.99)
The Eheim Classic filters are (arguably) the most effective canister filters on the market for "normal size" tanks. I don't like the clamping system (I've had a 2211 blow its top and drain a tank for me), and they're not as easy to service as the Filstar or the C-360 would be, which is why I'd rank it below those filters, but purely from a filtration standpoint, this thing is the best of the three imo, and that may matter more to you than a little bit of additional hassle when you're servicing it.
- Marineland Magnum 350 Pro ($111.89)
Never owned one, but on paper they look good, they're relatively inexpensive, biowheels work well, and like the Eheim classics, the design has been around for years and tons of people swear by them. I'd be comfortable using one on my own tanks
- Eheim 2215 ($118.99)
All of the pros and cons of the 2217 in a smaller, cheaper package.
- Marineland C-220 ($128.99) or Rena Filstar XP2 ($155.99)
Again, basically the same as their larger siblings, but cheaper. Probably easier to service than either the 2215 or the Magnum, but not as efficient, either. I'd consider both of these undersized for a 55 (extremely so in the case of the C-220; I have one on a 20 gallon, I wouldn't go much larger than that with it) and if I bought either one I'd continue to run your existing HOB filter. The advantage they offer over a cheaper HOB like the Emperor 400 (further down the list) that could be run by itself is that they're pressurized (like almost all canister filters), so they'll typically run longer between cleanings and do a better job of removing fine particulate matter than a normal, unpressurized HOB unit will.
- Eheim 2213 ($88.99)
Same as the two larger models; definitely a better filter than the C-220, probably a better filter than the XP2, but harder to clean than either. Much cheaper than either one though. Again, I'd continue running the HOB alongside this filter.
- Marineland H.O.T. Magnum Pro ($89.99)
This is the smallest and cheapest canister filter I'd buy. I'm not 100% sure I'd be comfortable using it as the sole filter on the tank, but I might be. It's basically a downsized version of the Mag350 with a single biowheel instead of a double. The Emperor 400 and 350 (below) both have two biowheels, so they may do better with biological filtration than this, but this will still do chemical and mechanical filtration better than any HOB. As an alternative, there is the Rena Filstar XP1, which is $10 more, but it's only rated for tanks up to 45 gallons. I might buy the Marineland, but I'd probably skip the Rena and just buy the Emperor 400 and save the $40 towards a bigger, better canister purchase further down the road. Don't bother with the Marineland C-160, it's too small for your tank.
- Marineland Emperor 400 ($51.99)
I was looking at one of these in the store the other day. As a rule, I detest HOB filters (if you want to know why, my rant is
here); I'd actually seriously consider using this one for certain setups. It has a second set of media containers that you can put whatever you want in, and the biowheels are going to handle a 55 with no problem. It's not ideal, but it's dirt cheap and you won't do any better for anything like what this thing costs. I'd be comfortable running this as the only filter on that tank.
- Marineland Penguin 350 ($47.89)
Nearly identical to the Emperor 400, but slightly cheaper and doesn't have the second media basket I believe. Good alternative if you're buying locally and you can't find the Emperor or it's significantly more expensive, but if you order from the site I'm linking to or somewhere else with a similar pricing structure, you might as well pay the few $$ more for the 400.
- Fluval C4 ($69.49)
I was looking at these in the store the other day too. Never used one, but on paper they look pretty decent. I'd bet money that the Emperor/Penguin is better, so unless you can get a screaming good deal on this I wouldn't bother, but it's an option. I'd continue running your existing filter alongside it though.
- Marineland Emperor 280 ($49.99)
Smaller version of the 400 for almost the same price since the 400 is apparently on sale right now. Obviously it makes no sense to buy this when the 400 is a better filter and the same price, but I put it on the list just in case you have to buy locally or something. Like the C4, I'd recommend keeping your existing filter running alongside this one.
- Fluval AquaClear 70 ($53.99)
Again, not as good as the Emperors, and it's more expensive. It does have good media flexibility, and everyone loves them, but I don't think they're anything special. They have bypass issues like other HOBs and they don't do anything better (imo) than the Emperor is likely to. If you can get a really good deal on one it'd be fine though, as long as you continued running your existing filter alongside it.
- Marineland Penguin 150 ($27.99)
Good as a supplemental filter to your existing unit only. Definitely not going to handle the tank by itself, but it's cheap and it'll do a decent job of helping out the existing filter.
- Fluval AquaClear 50 ($39.99)
Same deal as the Penguin 150; too small to handle the tank by itself, but alongside your existing filter it'll be an improvement. The ACs have better media flexibility than the Penguins, but I like BioWheel better than the sponges that the ACs use for biofiltration. This and the Penguin 150 are absolutely the smallest filters I'd buy for that tank and should be considered only if you just can't afford anything bigger.
Any of those are decent filters. Depending on what your definition of limited is, if it were my money I'd buy the Mag350 or the 2215; if those are too expensive, the 2213 or the H.O.T, and if those are too expensive the Emperor 400. I wouldn't personally spend my own money on anything else on that list save for maybe the Filstars, but they're all adequate filters that will do what you need either by themselves or in combination with your existing filter.
For some people that's $25, for other people it's $500.