jbk, you might want to check at king soopers -- when I was in the other day, they had energizer 2,xxx mah aa nimh batteries on sale for a real cheap price (can't remember specific on this though) and a charger on sale for a insanely cheap price (under $10?)
Also, if memory serves, some mp2s need to be modded to accept nimh (@ 1.2 volts per cell) rather than 1.5 volt per cell alkalines.
Regardless, I strongly recommend buying enough batteries so you can switch in a fresh set at set-break. While you can probably squeeze an entire show out of a single set of batteries, much better (imho) to not have to worry 'bout a sub-par charge late in the second set.
Despite my king soopers/everready notes above, have had great experiences with the maha charger and batteries I purchased from thomas distributing.