The prices have dropped by a huge amount, and you can get a nice projector for fairly cheap, but you still have the traditional problems with black values and contrast because it's existing technologies that have been out for a long time. The newer technologies are solving the contrast, etc., quite well, but still use a very expensive bulb because it takes a shitload of light to shine though a really tiny pixel panel and onto a big wall with acceptable brightness. The laser illumination technology solves that problem (and the bulb life problem, kinda...), but the laser illum technology is new and expensive. This isn't a bunch of milliwatt Chinese laser pointers thrown in a box...
Plus, the 4k has all of the same problems to solve but with a lot more pixel density thrown in the mix.
So projectors themselves aren't very expensive, but good projectors are expensive. It's not any different from TVs. You can get a really cheap TV with marginal quality, or you can get a really nice expensive curved-screen 4k TV for many times that amount.
