Ouch!! That seems a little high to me. You ought to be able to get a good job for between 12k-16k.
I install alside products, which are a good window and a good company to do business with, and at 21k I could afford to come from out of state and stay at a ritzy hotel while doing the job, then pay for all my christmas shopping and still take an extra few days off at christmas
Try to get 3 estimates, theres alot of good window brands and companies out there. It helps also if you can take the time to check a few references from the company you pick.