I traded a couple old airsoft guns sitting in my closet, value maybe $100 total if I'm lucky, for a cheap black powder revolver(~$150), which I then traded for a 125 with stand, kinda busted up glass tops, lights, undergravel flter, ~150lbs of pink gravel(lol), 3 powerheads(402 I think), a ton of fake plants, numerous castle decorations, 4 heaters of various wattage, 4 or 5 air pumps with tons of tubing(some still in the package), 2 bubbler/led
volcano decorations, various conditioners and fish food, several fish nets, and probably more I'm forgetting. Honestly most of the stuff is useless to me as I'll be going a different route with lighting, filtration, substrate, etc., but I've already managed to use a heater and some of the decorations in a smaller tank I've setup for my gf(more on that in a moment) and I'm sure I'll make use of the heaters at least in the 125. Honestly though I'm just thrilled to have gotten a 125 gallon tank in fantastic condition with a nice solid stand for useless stuff taking up space in the back of my closet.
As for my gf's tank, I got her a 16 gallon bowfront with stand, top and Top Fin 30 filter which works great for $40. All of it is in near new condition and I basically just had to buy a $20 light hood and the gravel of her choice, along with using the heater and decorations from my earlier 125 purchase and voila, full setup.
Just about a week ago I picked up a full 10 gallon setup for my friend's Christmas present for $20. It's just one of those Tetra setups that can be bought new for $30, but also came with a heater, glass hang-inside thermometer, attractive natural gravel, a few nice ~6" black lava rocks, a net, and a decent paper background. I'm gonna build a nice background/cave out of slate I already have in the garage as I find regular backgrounds and decorations to be boring.
That's all I've bought so far, but I see tempting deals all the time like a 55 with just about everything from stand to filter to lighting for $50 obo and another 125 with a nice dark stained wood stand for $130 obo. There is definitely a ton of money to be saved if one is willing to browse Craigslist regularly and put a little elbow grease into a project. I've been spoiled by seeing these prices and every time I go into a pet store and see $100+ prices on medium sized tanks(30 or what have you) with absolutely nothing else(let alone $700-800 for a 125!), I just cringe and wonder who is crazy enough to spend that much! I'm always thankful that someone out there is willing to buy new though so I can enjoy the amazing deals in the end and support my hobby without going bankrupt.