Fair enough. But the Milltek was also adopted by Vauxhall for the VXR220 (as an optional extra) and the Milltek range adopted by Vauxhall for the entire VXR range so I guess you could say that the manufacturer likes it. The Milltek was also destruction tested by Lotus, power tested by Lotus and Vauxhall and proven gains (by Lotus at Hethel) of 16-20bhpSame applies for other mid engine'd cars though. I've got an MR2 turbo which obviously has a similar exhaust setup to a VX and none of the exhausts are anywhere near the price of a Milltek, not even the crazy expensive Jap ones like Nur Specs.
...and thats why its expensive. The level of development thats gone into this system (and its proven power gains) is significant.it's not like there's a huge distance from the engine to rear bumper is it
Sure the Milltek might be good, but then again so is a Nur Spec (and Mongoose if you want to include it)

I've no idea what race cats Mongoose use. Milltek only use HJS motorsport spec cats, these are different and significantly better than a non motorsport cat (just becuse its xxx cell doesn't mean they are the same) and these are expensive. I'm not trying to slag off any other system, just offer reasons why the Milltek is not expensive for what you get.