Belz...
Fiend God
You make it sound complicated. I charge $70 for a service. If my customer wanted to pay in bitcoins, I would look up preev.com, see that the price (as I am typing this) is $134.5, whip out my calculator and say the price is 0.52 BTC. I would also expect the customer to add 0.005 BTC to the total so the transaction gets verified quicker.
The point is that if the customer makes the calculation when he orders the pizza, the price in BTC might be completely different when the time comes to pay up, etc.