I admit that I based my "guesstimate" on a sale I made several years ago. I had a very nice pair of straight TR3 front fenders, each needing only a relatively small amount of patching at the bottom. I got $400 for the pair, and I honestly wouldn't have taken much less. Admittedly, the buyer had driven down from somewhere in Ontario, Canada, to my house near Albany, NY, and he likely figured "what the hey...I've come this far"!
Oh, and I've also seen "new" fenders that, indeed, bore a passing resemblance to originals in overall shape but might as well have been for a Humber Super Snipe. Without an amazing amount of work, they'd never fit an otherwise straight, original TR!