In that case get a Rotax one. Look for a CRG or TonyKart frame. About a grand will get you one with some spares and a trolley on eBay.

There's lots of kart tracks that run open pit lane days for £30-50 so it's not too bad if you do it once a month or so. "Generally" people are friendly but get into racing and some people are stupid and will punt you off, safe in the knowledge they know the circuit owners better than you and won't be penalised. (Are you listening Lydd!)