Had trouble closing the left rear door on my 89 300se due to a worn door strike.

Was too lazy so took it to my favorite shop. Got the bill: $120 for the part! Good thing he only charged me $20 for labor.
Thinking this might have been a misquote on price, I called up Greenway Mercedes in town, a place known for high-priced parts, and got a quote fpr $216 to order the part. Finally I logged on here and found the part on-line for $40.
Expensive lesson learned. But, can anyone explain the wide range of prices?