Here's my $0.02
If you're an amateur ditch banger(aka not a pro snoX racer) I would stay away from the rev chassis(personal opinion here) because I'd be afraid of making a mistake, landing wrong, and bending the nun. So I'd look for an 08+ snopro 600 or an 08+ IQr 600. I know I can beat the piss out of my 07 IQr and not have to worry about breaking anything.
Sledneck is right, you're probably not going to find an RR for under 5k, but you will be able to find a good 08 IQr 600(factory) or a converted IQr (07 or <)600 for under 5k.
As always, I wouldn't listen to "sledcrusher", why settle for a trail sled and eventually wish you had a stronger sled when you can get a race sled and not have to ever worry about breaking it.