In looking at outsourcing contracts, if you like the company you are working with, you hope to develop a long term relationship.  Keep that in mind when you draft your contract.  You need to establish benchmarks.

To avoid paying too much, include a mechanism to measure market price benchmarks to allow your prices to go down, if the market dictates.  This will allow you to avoid being locked into a disadvantageous agreement.  Otherwise, years may go down without you realizing that you have been overpaying…and it will be too late.