if its for a 4 year old i'd recomemend one of these

http://www.youtube.com/watch?v=H8FFmSyEI40

only £34 posted of the bay,

http://www.ebay.co.uk/itm/TOMY-71706-GX-Buggy-Red-/330643165507?pt=UK_Toys_Creative_Educational_RL&ha sh=item4cfbde5143.

it's unlikely you'll buy a tamiya or other 10th scale for under £100 new.

loads of information on racing and buying 10th scale buggys here:

http://www.oople.com/rc/