how come telescope binocular is even more expensive then a telescope?

Two reasons:
1) As has already been mentioned, you have two telescopes -- most significantly, you have two sizable objective lenses, and large high-quality lenses are expensive.
2) With binoculars, you have to have a well-constructed mechanism to allow them to flex (in order to match people with different eye separations) while maintaining parallelism between the two optical units to a very high precision. For astronomical binoculars with high power, the specs for parallelism are particularly tight; and the heavy weight of these binoculars makes the mechanical linkage even more expensive.

Astronomical binoculars aren't necessarily more expensive than a telescope, but I think the above reasons explain why they are expensive.

Why shouldn't it be more expensive? It's like buying two telescopes.

Binocular telescope is two telescope in one focussed to a common centre line