dclegg:graemeh: Don't forget to tell your customer you are going to have to charge them 3.4% more to cover the pay pal fees!
It may not be as simple as that, and I may have to write this off as a cost of doing business with them. I've also not charged previous clients for fees incurred for having invoice payments transferred to me.
That's obviously a business decision that you need to make. You did say that your original agreement with them was for a wire transfer. If they want to change that part of the agreement then the whole agreement is up for renegotiation and that includes the price.
Is it an option for you to get a US bank account? Depending on the amounts involved there are better (i.e. cheaper) methods for moving money than your standard TT.