First, decide whether you want to make these quilts. It's okay to say NO. If you do, and if you're not going to be making them as a 'labor of love' (meaning you want to generate real income from the work), try to estimate how many hours it will take you for a typical simple quilt design, determine an hourly rate that you would be happy with, estimate how much the materials (including batting and thread) will cost for that design, add in the cost of a longarmer if necessary, and without going too much further present him/her with those figures as a rough estimate. That will probably end the discussion, as most people don't realize the true cost of making a quilt. If your customer is still interested, refine the estimates for the specific designs the customer wants, require 50% down payment, write up a contract stating when the quilts are due and when each will be paid for in full, etc. - and get busy! It might be best to start with an agreement to make just one of the quilts rather than all 4, so you and your customer can decide whether you're happy with the arrangement.