Why is the 2009 Ford Focus RS so expensive?

I'm looking for my second car, as my main life goal is to have a sick *** ride. I've been considering a few, with my top choice between a 2010 Subaru WRX STI (hatch) and the 2009 Ford Focus ST. I want to pay just a shade over 10k, but i will easily let 20K if i feel that me and the car make that 'connection' Obviously both cars are nearing 20k, and tbh i don't really want to pay that much, but these are both cars i've wanted since their release, when i didn't even have a full drivers licence. What i don't understand is why the Focus RS is so expensive? I can understand the RS500 due to not many being made, but i don't understand with the normal RS model. Another car i have been considering is a 2009 Astra VXR. Any thoughts?

Also if anyone has any good ideas for nice cars that are in the 10-20k range (the lower the better) that would be pretty awesome, and obviously i know quality comes at a price - that i would be willing to pay for. Anyway, i have a few more years of saving yet to get past the 20k mark so circumstances are likely to change as car price will go down and other things might pick my fancy. I was just trying to get some info on these cars and second opinions

Have you looked at the RS model compared to the ST.

The heritage in the RS models. Its a 300bhp hot hatch that is well capable of 350 bhp via the front wheels. Its a fantastic car. The ST is just no were near the RS and with the standard RS only having around 4000 units brought to the UK a very rare car.