In all fairness, CL deals depend highly on location. So, lets not get anybody's hopes up too high.
And yes, more water volume is pretty much always better when dealing with fish tanks. In your space, if you could fit a 75g, I would personally do that if you could find a cheap one. If not, a 40b is a great layout of a tank with lots of floor space. Some people dislike the 55g because it is rather narrow and not the most efficient use of the water volume. But, that depends on your personal preference.
In the area I live in now, I had to struggle for months to find a large, affordable tank. I eventually got a 75g with stand and everything for 200 bucks. In the last place I lived in, the town was small and used tanks were few and far between. So, it does depend on where you are at and what is available used. That is still absolutely what I recommend doing first. Just know that most used tanks come with terrible neon gravel and a plethora of useless airpumps and bubblers ect.