What to charge is always a thorny issue.
I charge what I feel is a reasonable amount based on my level of knowledge, capability to deliver and a lot of other factors. Some people charge more, others less.
Since your friend has been approached, why not ask the ones who did the approaching to make an offer from which to base negotiation ?
Flash is potentially in for an even rougher ride than this last couple of years has brought it. It went from hugely popular (and vastly misused) to almost ostracised within a relatively short period. Happily, it is expanding into different directions to include dynamic data handling and, more impressive, as a development platform for media output other than on the web.
Frankly, I'm surprised your friend was approached with this sort of offer at all. Flash animators have had a hard time of it this last couple of years and there are more banner resources (and experienced designers who can create artwork) than you can shake a stick at.
Difficult questions and almost impossible to answer.