For handheld under $500, try Saelig.com, and CircuitSpecialists.com
Both carry items in that price range.
I have the Owon HDS3102M-N, but that's $750 or so for the 100Mhz. It will be a lot less for a 20Mhz model if that will meet your needs.
One thing to watch for on handhelds, some of the lower price ones are only 1 channel. I'm sure that can be useful, but I made sure I was only choosing among 2 channel units.
I recommend watching Mike's videos to get a feel for this type of device. Good luck on your choice.