For anyone that's saying it only takes 1-2 days, if that, for Dre to make a beat I think you're being a bit presumptuous. I'm sure he could knock them out that quickly if he wanted to, but I bet that a lot of the time he won't be happy with it and spends a bit of time tweaking it. Just depends on the beat I'm guessing. Some he may be able to do in one go, say half a day, and others he might be working on for ages or leave and go back to them later.
As for the prices, from all the lil bits and pieces I've heard, $250,000 seems to be the price for his bigger beats. Although from some of the stuff that's been said in this thread, those in the Shady/Aftermath/G-Unit camp probably get them cheaper.