Most places online have it advertised for $450. Many of them have been out of stock on the carpet spec cars for a while now. The place you were thinking of may have been SpeedZone RC
which had it listed for $405. It is still
out of stock.
Seriously, though, you don't need
the carpet spec version. The only things not in the UK spec kit are the silver spring kit ($18) and the thick upper chassis plate ($24). The UK kit is $400, even, and it comes with the 75% arms and 1.3mm pistons. Buy the black spring kit (rubber tire) or the silver spring kit (foam tire) on your own, and the thicker top deck if you still think you need it after you build the kit. Remember, the stock chassis is a tick under 3mm thick, which is the thickness of the "custom" chassis made for Rienhard's 415 foam car for Vegas. It is PLENTY stiff as it is. And it's a few bucks cheaper if you do the UK kit, and add the other parts.
I would suggest the UK-spec kit, and take the rest of the cash and buy (20) 3.5mm ceramic diff balls and a spring kit of your choice. You should have just enough cash left to buy a Rubberneck bumper or one of those cool RDX car stands from Corally USA.