#3
if you want reasonably priced the headrush isnt the way to go.

Look around for a used RC-2 because the newer RC-3's are starting to hit the market the price of the older ones will come down a long way
#4
Depends on what you mean by backing track, how long, and how cheap. The Jamman series have plenty of storage for backing tracks. If you only want ~20sec of temporary storage then you can get something like an RP155 used for about $60.

The clip Sneaky in my profile was done in real time with a ME-25, which has 38 sec of temp storage.