I live within walking distance of 4 bike shops. If I'm feeling extra keen I will take the wheels off and take them in with the tyres. Otherwise ride the bike in, walk home, return with tyres, go home have a coffee, walk back an hour later and pick up bike. By the way, tyres arrived in Australia yesterday morning, cleared customs last night and should be delivered today. Unless I go to one of the big dealers that charge through the nose I would have had to wait longer for a local shop to order them. Even if I was only saving $20 I'd still consider doing it my way. The fact I'm saving $150 makes it a no-brainer for me.
I'd be surprised to see many of the Metro workshops charging < $100/h, JNO, and he said he dropped the bike off, then went back an hour later and picked it up. So there's yer hourly rate, more or less. A competent mech would have the job done in 30 - 40mins, yielding a better rate again.
I have been changing my own tyres (and some mates) for the last few years. Needed to get some gear to do it (all manual stuff), but I save $250 or more a time (including freight). Since I am doing 35,000kms or more a year lately, 2 1/2 sets of tyres a year makes up some saving. Cost is not the only reason as I prefer to do things myself if possible and do other maintenance while I am at it.