I am not willing to quote your work for you but I would decide where you are going to source your plastisol transfers and use the pricing they provide as a starting point. Add your shirt value and any mark-up you want to those two and then decide how much you want to charge for your time and equipment. I try to get at least a couple bucks per press cycle on small volumes like you will be having on those. Biggest thing with transfers are figuring out how many to order, and generally the more you order the more cost effective they become. Every time I do a small order invariably several more parents see them and want one too. I usually buy several more than needed (like a dozen or even more sometimes) and spread the cost out over the whole original order, then when grandma and the two crazy cousins want one you get to charge full price on transfers that are already paid for and if no one does then you aren't out anything.