How are Caterhams so expensive?

I'm looking for a fun car for the weekend that I can take on track. A Caterham seems like an obvious choice so I have a quick look on their website.

How much can a chassis that has been in production for 70 years with a Ford Focus engine chucked in it cost? 20k? 25k maybe with some options?

What was that? Sorry? Did you say 43.5k? For a car with no doors? Are you mad?

Well at least you've got supercar performance right, it weighs the same as a large motorbike so it should perform like one. Is that right? 0-60 in almost 5 seconds? So it costs the same as a Golf R and isn't any quicker despite being a third of the weight? Yeah, no thanks.