This has been discussed before. As with quilting service, the price varies by geographic area. Check with local long arm quilters, guilds and LQSs in your area. You can also look at online services. Binders usually charge per inch, with additional charges for cutting the binding etc. Also different prices for hand or machine binding. Here's one of the previous discussions.
http://www.quiltingboard.com/main-f1...es-t99211.html