a 'basic' starting place is to add up the cost of all of your materials---fabric, thread, patterns, batting, quilting charge---then multiply the total by 3---that amount can be adjusted as you feel necessary-
also you should visit some sites that sell quilts and see what going prices are---location matters---the market varies across the country just like the cost of materials ect-
there is a web site called ' quiltsforsale.com
visit there & browse the quilts/styles/sizes/prices. also some quilt shops (the cotton patch quilt shoppe in east tawas michigan is one) that have quilts for sale on their site- you call look at those too- to get an idea-
when people ask me about making them a quilt i generally reply- a queen starts at $350 & goes up from there- what did you have in mind? some people talk to me further about what they have in mind- some walk away shaking their head- some reply- i could get one at walmart for under $100---i tell them- that's nice- enjoy it..