Costs of materials is one thing ... and don't forget all the supplies that are used. It's not just fabric!
Your time ... consider how long you take to make a quilt. At $50 ... can you make that quilt in just 2 or 3 hours? Unless it is a very basic one, I doubt it! And even the simpler ones still take time thru to the end of sewing on the binding!
Next time you make a quilt, track how many hours ... it'll be an eye opener!!
And don't forget washing the fabric and cutting it out ready to sew ... all takes time!