I check spoke tension after about 250-500 mile, and then maybe twice a year(about every 7000 miles).

The $150 estimate is $120 for the rim & $30 for labor.

Mavic can be a pain in the ass to deal with, so you may need to find a good shop and have them order it. $120 for the rim is just a guess, but it's based on the fact that aluminum rims rarely(if ever) sell for more than that.

I don't think you are way too heavy for those wheels, but if the roads in your area suck, that would make a difference. It Phoenix the roads aren't too bad. Some very rough chipseal, but no frost heaves or potholes.