My suggestion (for what it's worth) is to check craigslist as often as possible to get a "feel" for what things sell for. I don't pay over $1.00/gal for glass tanks no matter what size they are because I've seen too many good deals. Good things come to those who wait. For acrylic... my ventures on craigslist rarely find a tank less than $3.00/gal but it does happen. I just bought 14 acrylic tanks on two petco stands for $80. For filters, lighting, stands...I cut their original prices in half, regardless of what it is. Note that bowfront, hexagonal, built-in sump tanks, etc will go for more money....how much you're willing to pay is really up to you. Put in your time and you'll get a feel for it.
Thats my 2cents... it might not have been what you were looking for and I'm not a dealer of any sorts but I've spent more hours on craigslist than I care to admit to. Many people have their own opinions on this. Especially if what you want is rare (i.e. an uncommon tank size).
One last note....when purchasing something, you should figure in the gas that it takes to get there too! Gas is becoming a major killer in my great deals.
Hope that helped somewhat.
