For an estimate only. I have a Sept 28 Phaeton that received its AACA Sr. in 1990. Has been driven to Hershey most every year since and has received 12 preservation awards at Hershey. I quit showing it at Hershey 2 years after they moved the show field from around the old stadium but has been by my swap meet space most every year since. It is showing some wear, but is still presentable, runs and drives well and have put over 15, 000 miles on it. The only thing I changed was it now has a Brumfield 5.9 head. About 5 years ago I was offered $32K at Hershey for it - was not for sale. Realistically, it is probably worth around $30K but would not sell it for that.
NOTE: For the most part the Phaetons are rare and desirable as compared to the other body styles. Depending on your location, with a Phaeton it is not so much the price but more if you can find one.
Hope this helps,
Frank