True Retail Price - Raw Coin

Theoretically the value for a coin at a given grade should be the same whether it is graded or not. All the grading does is confirm (according to the TPG's opinion) the grade. So an AU58 coin is worth AU58 prices regardless of if it is slabbed or not.

However, the grading does remove all doubt (aside from TPG subjectivity of course), provides an actual monetary guarantee with the top tier TPGs, and also the slab provides some physical protection worth a few bucks. So a graded coin will generally be priced much higher than a raw one as it removes a significant amount of grading risk.

Another technical issue is that higher quality coins will tend to get slabbed at some point in their careers and stay slabbed while lower quality coins will remain raw. So with coins that have a finite number available, the probability of a raw coin being high quality (not cleaned, tooled, altered, counterfeit, etc.) decreases each day.

Of course the retail price depends on what a retail customer is willing to pay.

I use [all of these for each coin I look at] ebay sold listings, Numismedia, Heritage Auctions, NGC coin explorer, USAcoin book. The variance is tremendous but you get an idea of absolute ranges and relative values between coins and grades. PCGS has an online price guide but the values seem to be grossly inflated.

Almost no one will pay for a proof coin as if it were graded anything higher than PF 65 when raw. There is just too much risk in the added premium.