No idea what to pay - I'm in Australia - but half retail is a good rule of thumb for anything second hand.

You just have to have a rattle gun (impact driver) for loosening anything, especially wheel nuts. Don't use it for tightening because they don't have torque control.
I've also got a right angle rattle gun - handy in awkward places.
An air chisel can be useful, but probably not worth the money.
Cheaps as chips, but really useful is one of the high speed die grinders. I've found they seem to use an aweful lot of air, so with a 15cfm compressor I can't use mine continuously, but they are good.
If you are doing any body work, an airpowered longboard is a godsend.

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JohnH