Well, there's a few reasons that I can think of:

1. Cost of molds, there are far more molds to be made for a jet than most aerobatic airplanes. Most aerobatic airplanes are limited to a cowl and wheel pants for fiberglass parts. Molds are expensive to make, that cost finds it's way into the kit.

2. Limited market, for every one jet that is sold, there are probably 10 or more aerobatic airplanes sold. Look back to point number 1, that means that the cost of the molds being divided into the kits has to be higher per aircraft than if it was an aerobatic prop job. This is probably the reason that even an ARF wood built jet like you show above is so much more money. Limited market......

3. Structure, there is typically more composite materials used in the jets, not always, but typically.

4. Time to produce. Fiberglass models are still layed up by hand, not computer built. In an aerobatic airplane, all the wood is laser cut, die cut etc. Yes it still has to be assembled, but so does the jet. There is probably far more time involved in assembling a jet kit at the factory than a Yak 54.

5. Finishing methods, if you're comparing an ARF to an ARF, painted jets, be it in the mold or out of the mold is more expensive than plastic iron on film. Probably more time consuming too.


If you compare a giant scale plane from Composite ARF or 3W, you'll be hard pressed to find a $500 one, they are up there with the cost of jets.
Heck, you really wanna see expensive, look at some of the new 2M pattern planes, they are as much or more than jets with 1/4 of the pieces.

That's not to say that jets are a good deal, some of them are certainly very expensive for what you receive compared to others, but I think part of the cost of a composite jet is in the idea that they are sort of the "ferrari" of the RC world, and you pay for that priviledge, it may not be right, but it is what it is.

Just my 2 cents anyway