I would tell them "I would be happy to make one/them for you, fabric and other supplies will cost $xx and labour will be $yy for a total of $zz. What kind of colours/theme do you have in mind?" If they really want it, they'll pay. And if they don't, no skin off your back.
That is assuming that you *would* be happy to make them for sale...if not, I'd just tell them - like my father in law does about his BEAUTIFUL wood working - "This is my *hobby*. I make things for my family and friends because I like and want to. I cannot afford to do it for free for every 'friend of a friend'. I do not want to be paid for it or for this to become a job, I have one already."