Where you go and how much it costs depends on how much you want the bottom end lightened. There should be someone local to you who could balance everything and maybe lighten a little bit at a fraction of the cost you mention. If you want it lightened a lot, then you need advice from someone who has had this done and then regularly revs to 7500-8000 rpm to prove it is still strong enough!
Don't waste time having the flywheel lightened, Rob at Sprintspeed ( www.sprintspeed.co.uk ) does one and also sells a good twin plate clutch and centre release bearing. I have those on my car and can recommend them (but you need a LSD of course).
