Sadly you are reading the thread correctly, car seats are expensive items in the UK, the maxicosy seat I use in my Nissan pick up or the Audi A4 cost £159.00 so about $300 and that wasn't the most expensive seat on the market, ok not the cheapest but at the lower end of the market
Another alternative is that I purchase a kit to be fitted to the crossfire which allows the airbag to be switched off, this kit from Porsche costs approx £500 + the cost of fitting, Porsche make no guarantee that the kit would work on the crossfire but the service manager did think it wouldn't be a problem, so if it did work ok I would be able to use any car seat in the crossfire, i.e. a £150 one.
Porsche also sell the same car seat as Mercedes with a transponder fitted but Porsche branded and they retail at £550 in the UK.

I agree its a rip off!!!

The real killer for me is that the crossfire I purchased in the UK came with a US handbook, I spent ages looking for the cup holder!!! bizarrely that was the thing I missed most when upgrading from the PT Cruiser to the Crossfire