It's a while since I had to keep a PPL current as I now fly commercial, but if I remember rightly you need to do minimum 12 hours flying per year in order to revalidate your license "by experience" - or else it's a check-ride with an instructor. I'm sure someone on here will correct me but it's something like that!
I had one or two years where I was only able to fly the bare minimum due to money (around 12 hours = £1000 of flying in a Cessna) and it was ok BUT I was a member at a very active club which had lots of fly-outs. I was often able to join other pilots in the right seat (and of course offer to pay for lunch and landing fees) and in turn they would be happy for me to do the radio and map-read which kept me "in the game" so to speak.
I also teamed up with other members where possible for days out: for example Essex - Isle of Wight is 1 hour flying time in a Cessna = £100ish and then the other guy can fly back after a nice day out and some time for lunch. If you do that alone, then of course it's 2 hours in the logbook but it starts to become an expensive day out...