Price wise, have a look at
www.karting.co.uk as they have a classified section in there, with various classes of karts for sale.
Also have the tracks, so you can see where they are, and then you can go and see how a race meeting is run, and talk to the people at the track.they will be best to offer advice.
apart from that there is the club100 championship, where you will need about £1500 a year to run in the 11 race meetings. The karts are a tad slower than having your own but you do not have to worry about the costs of cleaning, spares, maintenance etc.
Hope that helps a bit