For a non-prehung door, I don't think $250 is too high or too low. As for the cost of the door, well that depends. I can't speak to prices BUT I do know that if you can find the SAME door for less, Home Depot will 'match' the price AND give you an additional 10% off on the door (not the labor.) So, if you want to save a few $$$, check around about the Price Guarantee wherever you're buying the door.
My best to ya and hope this helps.
Jay J -Moderator
PS: You can always get a 2nd and 3rd 'outside quote' on your own to see how the labor comes out. There's a possibility that HD, for example, gets a 'kick-back' for getting a Contractor the job. But you can ask HD about that.