I think it varies depending on what type of person you are. A fair few people fall into the trap of paying £100s for an 'intensive' UCAT course which in reality only outlines the basics and a few tips and tricks which can be found via a quick google search. Most people on TSR recommend either Medify or Medentry (or both to get the best of both worlds). Their prices are generally cheaper than intensive courses, have massive question banks and mock papers to stimulate the real thing. It's recommended around 6-8 weeks of UCAT preparation so I'd buy either of those websites for a month or two.