That's how I've gotten all my tanks (6, including the 2 I'm picking up today) and so far I've spent only $130 on them. I paid for 3, and 3 I got for free. Ranging from a small 10g full setup for $50 (tank, cover, light, heater, filter, back when I was in a mad dash to get a second tank for my quarrelsome dwarf gourami), to the biggest one, 50g, also all inclusive for $80. One other wasn't free, but a barter situation.
The rest were all free, including my current 29g community tank.
And I'm not even listing the surplus of food, chemicals and other stuff that people threw in, some of which I've used, and some of which I've sold or given away too, because why not.
As long as you have space for it, to get a nice sized tank complete with light, filter and heater for under $100 is still a steal…as long as everything works and the tank doesn’t leak. I would also say that there will be more deals out there too though and sometimes looking for the next deal is fun too.