I bought a 5 gallon hex tank at walmart, and used that for my fry. I put some netting over the filter to keep them from getting sucked up. It was under 30 bucks, and fits almost anywhere. You could look on ebay and maybe find a small used tank too.
They can also stay in a small fish bowl. They can live there for a while without aeration (mine were in a bowl for 2 weeks and they survived).
As far as the living in with the big fish. I had a few that were in there for over a month in there and they were fine. They had a place to hide, but it is probably not the best place for them if you want them to live.
Good Luck!!