Zed's right here, but if I can make a suggestion: if you get requests like this, ASK FOR THE MONEY. If companies can get something for free, sure they'll try and do that, but if they want a patch, and it's going to be some work, send them back a quote for what you think would be fair. Add in some expense for the inevitable paperwork and make sure it's a number that you'll be happy with.

Sometime you just have to put the sales hat on and ask for the money to close the sale.