The common answer that I have been told for 4 years is $1 for every 1000 stitches, but that does not inclure the towels if you have to supply them. I am sure their are others that use embroidered items to make money who can give you a more up to date and indepth answer.
What would you be willing to pay for them? I know the going rate has been said to be 1.00 for every thousand, but if that was the case in my area, I wouldn't sell anything. You have to figure out what people in YOUR area are willing to pay for your items. I have had people tell me I do things to cheap, and the next one will come along and say 8.00 for that..With people like that, I just tell them that I'm not walmart. Somone told me that they could buy bibs cheaper at Target, and I told them, than that's where they should be. Think about what things in your area go for and charge around the same.