I never keep track and I can't really calculate the cost per quilt anyway. I have several "going" at one time, some of which take me years to complete. In the meantime, I buy fabric as I need it or as the mood hits me, all of which goes into my stash. When I pull fabric out for a quilt, it could be anywhere from brand new to 10-15 years (or more) old. For the most part, I buy everything I use for quilting at sale prices. I made 1 quilt last year for which I specifically bought all the fabric over a few weeks' time. Most of those fabrics were not a bargain so the total cost was high, but I had lots of those fabrics left over, from which I made a second quilt top and I still probably have enough for a couple more.