...Two things I’d like to replace on my car are one head light door (AN headlight) and an OEM locking gas cap. Both are so astronomically expensive that it’s rather comical...
Funny thing about parts prices. They are not going down. Oh, some mechanical parts that are routine maintenance items such as brake pads, etc. are reasonable and there are plenty of aftermarket versions available, but the proprietary parts are high and getting higher. So the bottom line is, if you want or need some proprietary part, don't stand around griping about the astronomical price, because while you do that it's going up.
I offer my own story of the [in]famous grill star and barrel. At the time I needed one in my restoration they were priced [new] somewhere near $250 or so, and I thought that to be high. So, my restorer found a used one somewhere for $75. The used one was good; not perfect, but it polished nicely. There was one bit of flaked off chrome on it noticable only to me. Meanwhile the prices of new ones kept going up and up and up. But, with the rest of my car having all freshly chromed or new trim, this star bothered me to no end. Lo and behold some member here lost to memory sent me a PM and offered me a NIB/NOS grill star and barrel for $300. I thought that was good, since the new ones from MB had now gone to over $350. So I bought it. In the time it took to get it, and install it a year later (yeah I don't move fast on some of this stuff) prices had risen again. I made the swap and received about what I paid for the new one, for the used on eBay! Meanwhile, back here a few years later the prices had risen to over $500 and those who needed this part were holding off on buying one, complaining about the price (as if magically it would go down).
Well the last time I broached the subject, Tom Hanson of the Classic Center told me that the last new one they sold was over $2,000 before they went NLA. I would like to think they will be made available again because they are fragile and they are proprietary, but I can assure you they won't be cheap! When I commenced my restoration in 1999, the Pagoda was just transitioning from an old car to a worthy collectible, so many parts were still reasonable. Nonetheless, it still took over 1,000 hours, not including sublet work such as brake restoration, plating, etc. There were tens of thousands of dollars of parts, at 1999-2001 prices. Labor was $45/hour. As they say, do the math...