Sub £250

Jessy

Well, first of all, if you are doing dirt jumping, DON'T GET AN XC FRAME! Geometry is personal preference, the main thing that sets apart dedicated jump frames is they are designed to take hits that would quickly destroy a cross country frame. Having a tough bike does wonders for rider confidence as well. Specialized have the P. series of bikes designed for jumping, I'm not sure how much they are though.

As for the second hand route, that Kona sounds like a good deal as they make excellent jump frames, although I'd check and see what materials were used: I'd be VERY wary about buying aluminium second hand as it has a limited lifespan and it's hard to tell how long it has left. It's stiff and doesn't rust but it will eventually snap. Steel is stronger and heavier, so a steel frame will be made with a lot less metal, and may be slightly flexible. A steel frame will in theory last a lifetime if properly taken care of, and when you finally damage it beyond repair it will probably be by you bending the tubes rather than surprise snapping, which is invaluable for dirt jumping IMHO! Also, with any frame, the strength will be reflected by the quality of the welding: Make sure the beads on the welds are closely packed with no pinholes. To check that the frame isn't bent, make sure the tubes line up when viewed from in front and above and that there is equal tire clearance on both sides of the wheel. If you are unsure about this just pop into a bike shop: They will be able to tell you in seconds if you have a dodgy frame.