If I contact a regular, I usually ask, "as usual?"
If a regular raises their price and waits until after the session to tell.you, you need to drop him.
EDIT In my experience, good regulars lock you in at the original price. I only had one regular who (twice) raised his price, and it eventually ended badly.
When it's a new guy, I always repeat the amount of time and amount when asking for the final agreement. The oral contract is made if he agrees.