We had our service upgraded in late '98 when we installed a new furnace. We went from 100 amp to 200 amp at a cost of about $1,350.00. This was for parts and labor, so I don't know what labor alone would have been. Note I live in northern California where prices tend to be a little higher than other parts of the US.
I'm not a home repair expert, but it sounds like the other posts gave great advice about having the contractor supply the parts. I take a Murphy's Law approach to doing projects, meaning that if anything goes wrong with your service upgrade, the contractor could blame it on the parts that you provided and stick you with additional costs. On projects like this you may save a little money by supplying the parts yourself, but it may not be worth it in the long run.
I also agree with the advice about getting box with more switch capacity than you think you need. My contractor installed a 20 switch pannel, and even though my house is small we are using up the switches pretty rapidly. It'll cost a lot more later if we need more capacity later, although I belive it is possible to use duplexed switches.