What do you consider "very expensive"?
I used the Orion RA/CI for a year or so and it didn't break my budget:
The 6x30 is ~$42 and the 9x50 is ~$66.
That's cheap, relatively speaking
RA/CI finders normally suffer from image degradation based on their optical design/number of optical elements,, and I believe that's why you don't see them offered by distributors, as opposed to price.
Also, IMNSHO, it's a niche product; many astronomers get used to the "upside" down effect.
Just flip your star charts and shine your red light underneath them to match the orientation ~~~
haha! wow, I forgot about that 9x50....pretty sad since I used to work for them and own that finder. Anyways, comparitively, the pricing is still a bit more than a normal upside down finder scope. A normal 6x30 finder sells for under $30, whereas a correct-image 6x30 sells for just over $40. Yes, in the world of photography, that isn't much at all....but I did find that with most customers in the Astronomy arena, that was a big determining factor in something that serves no purpose other than to center on an object (and I know from working in the industry that this was a very big reason why correct image finders are rarely if ever found as a standard item on a telescope....it keeps the price to the customer lower). They'd rather save that money and put it towards a better eyepiece or filters. BTW....I noticed someone recommending an erecting diagonal for the upside down finder scope....based on the finder scope in the picture, that is NOT an option. The diagonal would be used on the main telescope and based on the picture, the scope already has one. It may be mirror reversed, but it should be right side up in the telescope itself.