I believe somewhere along here, you said were in North Jersey? I went on CL, here are some that I found 100 gal+ up and under $600 (which is still VERY expensive I realize, holy cow are prices there HIGH!)
100 Gal (6 feet long)- $425 tank, stand, and canopy
http://newjersey.craigslist.org/hsh/2991617013.html
130 Gal (6 feet long)- $500 tank, stand, lights, filter
http://newjersey.craigslist.org/fuo/2981385768.html
125 Gal (fully set up with fish)- $600 or will trade, I believe you mentioned you had quads somewhere?
http://philadelphia.craigslist.org/bar/2990220870.html
(You'd obviously have to ask him to rehome the fish, or rehome them yourself)
180 Gal (just the tank itself, but you could build a stand I bet!)
http://newjersey.craigslist.org/pet/2920079656.html
125 Gal (tank, stand, custom light, and filter)- $500 OBO
http://jerseyshore.craigslist.org/for/2952311101.html
250 Gal (5 foot, tank, filter, and stand)- $500
http://newjersey.craigslist.org/for/2922947855.html
150 Gal (tank, canopy, stand, I think the filter too, 72") $550
http://newjersey.craigslist.org/for/2951605065.html
125 Gal (tank, hood, bulbs, etc.) $500
http://newjersey.craigslist.org/pet/2978532643.html
110 Gal (tank, lights, canister filter) $350 OBO
http://newjersey.craigslist.org/search/pet?query=aquarium&srchType=A
110 Gal (tank, hood, filter, and lights) $400 OBO
http://jerseyshore.craigslist.org/pet/2971350573.html
150 Gal (tank only no price listed)
http://newjersey.craigslist.org/pet/2977611246.html
Hopefully this helps a little bit if you don't want to make a tank. I can't get over how darn expensive everything is there!
Here's what $500 can get you where I live
http://fortcollins.craigslist.org/for/2980929196.html