I am assuming it is the "seat recognition switch" sensor that tells the air bag module whether or not to ignite the pass. side air bag. They are very common fault in the SRS system for 210 vehicles.

That price seems normal - not high or low.

As for cleaning the contact ring. The steering angle sensor provides continuity for the drivers front air bag. It is encased in plastic and can not be cleaned as could the contact ring on a 124 body style E.

If it is the pass. side seat recognition switch, the pass side seat cushion will need to be disassembled. Call and upholstry shop, many times they are a lot cheaper in labor - but you'll need to supply the part.