paul,dont bother getting pre-paid envelopes. i print my self addressed envelopes on my own computer and leave them with the customers.i have been doing this for about 3 years now and probably only had 3 or4 customers who have complained,to these customers i just say that if its that much of a concern for them ,they can knock the price of the stamp off the invoice,which none of them has ever done.i also have printed on the top of the envelope-please ensure we have your address and phone no -this way i know who the cheque is from and i have their no incase i need to contact them when payments are outstanding.