You should consider the total relationship with your mechanic. A small difference in the cost of having your mechanic changing the oil vs Jiffy Lube could pay off handsomely in savings on future maintenance. You mechanic will be more likely to point out things that need attention when they are less expensive to repair and maybe catch any safety related failures early.
I would caution you that if you think the mechanic is taking advantage of you, like it seems to cost $500 every time you visit, then find another mechanic. But if you have found a good honest mechanic, you should give him ALL your business.