Paying with Bitcoin is a choice really but if you aren't comfortable paying with Bitcoin because you think that you might be paying more, why not liquidate the coin to your legal tender and pay? Also, remember that at that particular period, you may be paying more or lesser using Bitcoin because its price is not static. 
My concern now is that if we then shy away from paying with Bitcoin, how do we create more awareness, adaptability, and acceptance of this coin? I will conclude by saying use your Bitcoin diplomatically.