Honestly, to not have limits on what you can grow in the bottom 1/2 of a 55g, you'd need to consider something other than T8 lighting. I would think that with enough T8 bulbs, you may be able to grow some moderate light SPS corals near the very top of the tank, but that's about it. Most soft corals and many lower to moderate light LPS would probably do fine under an adequete T8 set-up. If you want a clam or anemone, I'd highly recommend choosing some other lighting type.
By the time you piece together a DIY T8 set-up, a few extra dollars should get you a nice DIY T5 HO system. This, of course, assumes you'd be buying everything for either set-up -- endcaps, stand-offs, ballasts, bulbs, reflectors. The largest added expense would be in the individual reflectors for the T5s, as IceCap SLR reflectors run about $20 a piece. But, T8 bulbs don't readily come designed for reefs in 4' lengths, so you'd end up buying twice as many parts and bulbs (to run 2' bulbs; once you step up beyond 2' lengths bulbs for reefs tend to be T10 & T12), adding to your costs quite a bit.