From the way you worded it, it kinda sound like a favor/ little extra cash project. It's not like your doing this for a living, and considering if you brought it to bestbuy. It might cost you 100$, but consider how much of that money goes to the installer, and to the business...
I say 40$-50$...
I'm not sure about this truck, but to just REPLACE the speakers in my car (no new wire or anything) would take about 10 minutes...