Re: Cheap flying
I believe there is at least one 'no capital' group/aeroplane operating out of Elstree.
I understand you can fly Microlights on your PPL SEP; some conversion training is recommended though even if you stick to 3-axis microlights.
Gliding is cheapish but very time costly, I suspect that the big mortgage also means 'not too much spare time!'
Alternatives are glider tugging (although a lot of them do like you to have gliding experience} and hauling parachutists.