Good luck to you. I understand the ASAP thing. I just hate to see a great starter get replaced with one that could die young. The thing is you wouldn't need a replacement starter if all that's wrong is the contacts. Your mechanic could replace them in 10 minutes after pulling the starter out. This is all assuming that the contacts are the problem. Does it do nothing when you turn the key over and over and then finally start like there's nothing wrong? That's the classic bad contacts symptom.
1.5 hours seems very reasonable from what I've read. I have not done a starter on one of these but everyone says the 4WD's are a bear to get the starter out and back in so if that's all they are charging you I'd say you're doing alright.
Here's a write up to let you see what I'm talking about...
http://www.toyota-4runner.org/3rd-ge...tml#post530199