Just last week I got a quote from a mechanic to replace a bad sender unit in my 2005 Frontier. Was going to be ~$1300. said they had to replace the whole fuel pump ($500 part). I had researched it on the web and the part was $300-$400 OEM from the dealer, PLUS they said tranny, transfer case, oil (I knew that one needed changing), radiator, brakes, power steering fluids all needed replacing, as well as shocks and struts. This was on top of the $1300. Also, I told them it was the sender unit (a fault on 2005 Frontiers @ about 50K miles) but they charged me $160.00 for running a diagnostic. OH, and would take 2-3 days.
Had they wife call around==got an estimate of ~$800. Had the local garage do the fluids==didn't need replacement and they topped them off, lubed, flushed radiator for $200. The wife called around and found our old mechanic at a new location. He did it in 2-3 HOURS and replaced just the sender unit ($146.00) for a total of $510.00.
You really gotta be careful!