In a local racing scene(road racing/autocrossing/driving schools, say, about 3 states) what is a fair price for having sponsors' decals on your car? some people get services or end-products in return, if you calculate the sponsor's contribution in US$, how much would it be.
everyone's $0.02 cents is welcome, thanks!

You may get a discounted price on parts....they don't PAY you unless you are BIG TIME. Some of the time you get free stuff if you win with their decals on your car.

...with anybody but your accountant at the end of the year.....

...as in "zip" or "zilch" or "nada". As Steve mentioned, you might get a supplier to give you a break on parts & supplies, maybe throw in some freebie samples every know and then. Some companies have a contingency system that rewards performance - finish in the top 3 at a SCCA National race or Pro Solo event and they give you credit toward merchandise, etc., but at the local club race/autocross/driver's school level you won't see a thing.

And certainly don't believe what you hear in the paddock. Incredible BS generated by the Poseurs about the value of their decals. Roll up your pant legs.