All depends on what you put in it. A quality Power system could be near £300 or for budget stuff more like £150-180ish.
Add anything from £20-£90 for a servo up to the job then TX/RX unless you have one already, if not £150 will get you a good radio, £30 gets you a crap one. Just remember if you buy cheap you buy twice
Ah then you would need a body and wheels n tyres. So £30ish for shell plus paint £30. Wheels are about £12-£20 per set of 4 depending on brand etc, tyres also anything from £20 - £30 per set of 4 and you will also need inserts at £9 - £14 per set of 4.
Going middle of the road prices roughly £440 on top of the cost of the kit so £770 in all. Then just get spares as you go, or buy everything all in one hit
http://teamkirk.co.uk LOL as my slash has a ton of spares and upgrades