You're really not getting this mate.It doesn't matter which way you price it. In BTC or USD. If what you are doing takes 3-4 weeks to do, and the price is doubling or halving in that same period. Someone is winning and someone is losing hard. Especially if you need to pay other subcontractors in USD.
Even if you do really great work. If the person pays you, and then the value rises. They're going to feel ripped off.
Don't even look at the rate of exchange until the day of payment. Price it as "$100" (Payable in bitcoin) and then at the very instant it's time for them to pay, at THAT TIME ONLY show them the price of $100 worth of bitcoins to pay.
Without the prior thought of what $100 worth of btc equals, they won't have a comparison point.
Sadly this process will be useful until bitcoin stabilizes. Don't look for that stabilization for years, perhaps 2017 at the soonest.