IMHO, the 503 is worth $175 = $200+ all day long (my favorite 44 mould), the 68 not so much. The 503 may even bring a bit more because of condition. There are thousands of 68's out there so they are worth a bit less.
But, in an auction setting I have seen stupid money paid for some of these moulds, including the 503's and 51's. Some of the more uncommon moulds have gone for crazy money.
I know......I have done it.....I paid $200 for a pristine 10 cavity S55 some 30 years ago
I paid near $300 for a pristine 2 cavity FACTORY #51 dual hollow point. I was told by an H&G expert that is only the 2nd one he has ever seen, and he owns the other one.
Unless you vastly overpay for a pristine H&G (yes, I have done it), you will forget what you paid for it over time. In fact, you will have these moulds for the rest of your days, and hand them down to your kids.
Pay once, cry once, and use them in good health!