There are specs... and then there are specs
Any reputable sail loft will be able to quote a price based on the IJPE of the boat, which they'll have in their database. However, once ordered, you'll need to provide some measurements to the loft, i.e., from headstay to fairlead, mast to outhaul, etc. A loft that doesn't ask for some fairly specific measurements isn't making a sail for your boat, they're just cutting something generic that may not fit quite right.While I'm at it, you should check the prices on the Doyle sails in the chandlery here. They are built domestically and designed by some of the best guys in the business.