Do some research on the fabrics, patterns and techniques used and get a realistic date. Using the date and size, visit antique shops in your area and see what they have. Check completed listings on EBay. An "old quilt" made in China in the 80's is not going to be as valuable as an old quilt from 1880 in the same shape.
Spectacular quilts in great condition will get top prices; cutters are rarely worth more than ten or twenty bucks. You can't price an item on sentimental value. What you consider repairable, someone else may consider trash.
Online auctions and Craigslist will need good quality pictures (of overall quilt and any defects). Prices may be higher or lower online than they are locally. For your own protection, be prepared to accept PayPal if you use online auctions, and make sure you package the item appropriately for mailing..
Consignment shops often take up to half the sale price. Ads in newspapers can get you a quick sale, but bring strangers into your home. Flea markets are great if you have a bunch of stuff, but not really practical for a couple items.