I would agree with Brian. Visit flying clubs in your area. Most will have noticebaords or folders with club members selling planes or shares in planes. A look in the back of Pilot/Flyer etc... will give you an idea.
You should be able to buy a share in a respectable Piper/Cessna/similar for maybe £3-4K. Group payment structures vary, but you are likely to have a monthly payment, maybe £50-100 pcm, then the flying might come in at £50-60 per hour.
If you built 100 hours over 6 months and completely wrote off the capital outlay of say £4K, at £50 ph wet that works out at £9K plus monthy payments. Still less than the typical hire costs at usually well over £100 ph. If you got back say £2K on your share, you've probably saved a few grand.