Bit like watches, you pay anything from £100 to £3/4K, I go most weeks and just like being out in the country side but if I get something with history then it’s all the better.
Permission must be sought for most land in the UK, beaches are fine but you should log your details with the crown estate first.
I would look at the used market and something like a Garrett 250 will be good to start, around £150..