Since you're looking for "large", there are 100. 125, and 150g that have a 72" X 18" footprint, which will fit your space. But if you're going for used, you might have a tough time finding these. More likely that you'll find a 75g or 90g, which have 48" X 18" footprints (and a 3" height difference).
My city has about 270,000 people, and I was able to find a 90g for $100 (talked down from $150) with a couple powerheads, a broken heater, and a useless 2' T8 hood. If I were patient, I could probably (eventually) find the same bare tank, with stand, for $200 or less. In larger cities I would bet you'd find better deals. In smaller ones, it would likely be tougher.
However, with large tanks, it becomes increasingly important to place them against a load-bearing wall, perpendicular to floor joists. Something to keep in mind. With a 40g, as Nubster recommended, that wouldn't be an issue. With a 90g, it's something to think about. More than that and it's definitely an issue.
A couple other things to think about:
The most common bulb and fixture sizes are 2' and 4'. In addition, taller tanks are both more difficult to do maintenance on and tougher to light.
And, as far as CO2, DIY is doable with a 40g. Less so with a 90g. More than that, and don't bother - it's just too much effort to be fun anymore (okay, yeah, that's just my opinion, and some people will disagree, but really, it's a massive PITA).
Cost increases as size increases, obviously. But it's not a parallel relationship. A 40g setup, for example, costs less than twice as much as a 20g setup.
You need to pick a cost limit and work from there. For my 90g, which I have yet to set up, I figure on an investment of $500-700 for high light, generic substrate, decent filtration, and a DIY 2X4 / 2X6 / plywood stand. And that's before anything living ends up in the tank.