Not that expensive actually for all 4 wheels. And we're pretty much talking race-pads here, not just road pads.
If you go to a very good pad like the compound 97 made by Performance Friction in the US then you'll pay even more.
Oh... And expect a full set of regular pads from Lotus to fall in about the same price category. Around $250 to $300 for all 4 wheels.
If you do shop around for alternative pads you may need to get the friction material shaved down a little to fit between the disc and the calipher.
Total thickness for the front should be 14.3mm and rear 11.6mm (rears start out pretty thin when new..). There is some room to play (esp. at the back), but you'll have to find out in practice how much really.
Most performance shops can/will shave brake pads for you for a modest fee.
Bye, Arno.