The price of competing in the UK

From the people here from UK, going to bodybuilding comps. I would love to know, how much in general the "hobby" comes to. It sounds a really tempting idea, but I have the idea that you have to pay for each competition and all in all with bikini included gets to astronomical prices. Is there any "amateur" competitions or free ones where one can get into to get the feeling of it?? How much are the costs involved in the UK and what competitions are around?? Does anyone know what is available around London?? Sorry for so many questions, I am really curious as it is something I don't have a clue about.