My (friend's) mom's coworkers gave mom a betta fish, in the tiniest bowl possible, as a gift for something. Obviously they weren't prepared to have a fish, so the poor guy has been living in this horrendously tiny bowl. They don't have space for anything very big, and I offered to buy a larger tank for him, so I can't afford a whole lot, either. I've been watching Ebay, but for some reason most the 2.5 gallons run $20 or more. I don't want anything but a 2.5 or 5 gallon tank, no accesories necessary. I don't mind paying reasonable shipping. If anyone has one they could spare, that would be wonderful! Thanks so much!
I know this isn't a forum to give advice, but I would go with a 5 gallon... with a 5 gallon, you could possibly introduce a couple small fish. And you can get a good filter like a whisper 5-15 or something. Just a thought
There won't be any other fish! They didn't plan for or want this one, and it would be a miracle if they could keep any other fish, in addition to him, alive. And I don't think a filter is really necessary for one betta, so I won't worry about that too much.
Thank you, though, for your good advice. I actually hope to steal this betta eventually, if I get room at my house during his lifetime. If that becomes the case, THEN I'd go with something bigger in hopes of adding some small fish and doing things properly.
I've been keeping the single bettas without filters for about two years now, so I think it's working pretty well.
And goodness, I do wish I could be hooked! I have all my future tank setups planned out, just have to wait for the time, resources and space. My family's outgrown our house, so I'm really at loss for any space at all right now. Otherwise I'd have at least a 10 gallon setup, as well as some more bettas. Thank you for your help!
If anyone has one they could spare, that would be wonderful! Thanks so much! 
And I don't think a filter is really necessary for one betta, so I won't worry about that too much.
Thank you for your help!