Yeah, I couldn't even set up my daughter's 2 gal tank for under $30 and how many 5 year olds need a $30 fish tank in their bedroom? I guess it depends on how popular fish are where you live. I guess if they are not popular you can get a cheap tank. But not around here.
I've purchased new glass 10g tanks at petco for under $13. That is tank only not a complete kit. Yard sales are an awesome place to get complete setups for just a couple bucks, even if it's old used and dirty, it probably works like a champ.