800$-1,200$ for the stainless steel versions and 1,500$-2,400$ for titanium bits (lower prices are for single exhaust, twin-tips are more).
Yesterday an Aspen White Elise drove by me when I was downtown (I've only seen a handful over here), and I don't know for sure which exhaust it was using (2 Lotus models, Arqray, Quiksilver, Larini etc), but at low-mid RPM, I'm gonna have to admit it didn't sound amazing. It was a very flat and bassy noise. It would turn my head just by the noise, but I wouldn't expect a Lotus to be making it. But then again, I'm sure it sounds great when on cams.