tell me why

When your fan base's tagline is "Mopar or No Car" your parts are going to cost more.

A big part of the reason Mopar parts are more expensive is because they know Mopar guys will spend more for the same (or less) power than Chevy guys.

Even Mopar knows this. Look at the $$/HP ratio on the 500hp crate motors. You can get the same power for 1/3 the price with the other guys.

The fact that there are a lot fewer Mopars than Brand X means there are going to be more options for the other guys. If you're going to make a product, you want to sell a lot of them, so you make it for the big market.

I came from Ford stuff to Mopar, and it was a rude awakening as far as the expense goes. It costs a lot more to get the same ET out of an A-body vs. a Mustang. And there are much better aftermarket parts available for SBF than SBM, but, I wouldn't go back....

For me it came down to this: Which will make me happier; going fast, going fast as cheap as possible, or going fast in this car?

That said, I got creative with some junkyard parts (couldn't afford to build a small block after buying the car and building the transmission) and it turned out great. Though my ET aspirations were probably more modest than yours.