If you were to insure this with an insurance company for replacement value it would be VERY high. Get it appraised!
Like anything, there is the IRS tax value, donation value, actual cost, replacement cost, etc. Only a trained expert can answer your question. When you raffle the quilt you can advertise that it will come with copy of the appraised value so the winner can get it insured if they want. When people can see the REAL value you may sell lots more tickets. It's like buying a diamond ring= you'd pay more when you could see the actual expert certified appraisal.