If you really want to do this, take the "customer" along and have them pick and pay for the fabric, thread or whatever else is needed. That will be a shocker. Then set your price, remember you are using your electricity, new needles and thread.
I didn't knit at the time so I asked a neighbor to knit a sweater for me and she said "sure, the price is $300.00." I about fell over, and she said 'I really don't want to do it, but if you pay my price I will." No sweater for me.