Around here the labor rates hit $70-75 per hour. Based on that, they did about a 40-minute job and charged you a fair price--especially since they're making nothing on the part. I'd say thanks to them for being willing to work with you as they did; around here, I wouldn't expect that kind of indulgence from a good indie, let alone a dealer.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)