One months access is £40, two months is £45, the cost varies depending on how long you want to spend preparing. Most of the books you can buy are £20-25, but they don’t help you get used to doing it on the computer or to the time pressure. Many courses are over £100 for a day. There are free resources online that you can use too. The UKCAT website, medicportal and others have sections that can help. There are even videos that people have put on YouTube.
One of the things I liked on medify was that as you work through the exercises, if there’s a particular type of question that you’re weak at, it will signpost extra help for these and give you more of these questions, so you’re spending most time working on the bits you actually need the help with.