There's a lot of factors that go into prices. One concept that many people don't seem to understand or are aware of, is the investment costs of development and tooling and how the sale of the product needs to pay that outlay off. Those costs are relatively fixed, but the sales volumes can be all over the place. If I owned a repro parts company and was engineering a repro rear quarter for a '70 Coronet, a part many here would love to see I'm sure, the costs would be similar to the cost to engineer a repro rear quarter for a '69 Camaro. How would sales volume compare though? Maybe sell 50 Coronet quarters a year, but the one for the Camaro might sell 2000 a year. I might have to charge $2500 each for the Coronet quarter panel to justify the investment to release one to market. On the other hand, I might be able to sell the Camaro ones for $350 each and still have enough margin to make a tidy profit for my business.
Sadly there are far less Mopars out there, so the market for parts for them is proportionately less, and our parts have to sell for more than similar GM or Ford parts in order for the suppliers to be able to justify the investment.
That also ties in with why sometimes a needed part will come to market for our cars, then some years later, the part will be sold out, and not be available again. Your first run was 500 parts, which you had to pay up front, then it took 5 years to sell them all, while you paid storage costs to keep them somewhere gathering dust until they all sold. You then realize it's not worth the money to do another run.
It's getting bad out there for parts though, and frustrating. I bought one of Tony's repro 216 fans last summer for $235. Recently a member on another forum posted he was looking for a 216 fan, so I responded why not just buy one of Tony's, they are a really nice piece!
He said I don't want to pay $345 for one. Huh? I just paid $235 a few months earlier. So I check Tony's website and sure enough, they are $345. Then the guy posts again this week they are now $385. So the price went up about 2/3rds in just over 6 months.
When I bought mine, I seem to remember there was something suggesting low inventory of the item, so I'm guessing Tony placed an order for another batch, and for whatever reason the price he had to pay for them has jumped considerably. I'm sure Tony didn't raise the price just to pad his bank account. But price increases like that are going to cut the already small demand for Mopar repro parts and make it less likely we'll see new needed items introduced, and more likely items available now will not be available any longer in the near future.