Also if you're on a budget, be aware that it's not just purchasing a tank, it's also filters, sump, plumbing, pumps, heaters/controllers, substrate, etc... Even going the cheap cheap canister route you'll need three for a big tank plus associated media. Craigslist really depends where you live, big tanks here in the middle of the country are extremely rare and just as expensive as new usually (or really stupid dimensions) while on either coast they seem to be a dime a dozen.
Midwest checking in... I plan on purchasing an FX-6 for filtration - separate from the Tank budget. I just wanted to make sure I get a good tank that'll last me a while. I got my current 75g from Petco, i'm slowly noticing the flaws after a few months.