Price Estimate For Stereo?

As you may have seen in a previous question, I am the owner of a 77 silverado tha has the original stereo in it. I'm planning on taking that out and putting in a new, Pioneer stereo (one of the normal, thin ones, not the double din big *** ones) but need to cut the slot wider. I figure the stereo itself is around 100 bucks, but any ideas on how much the cutting/installation might cost?