£50k will these days get you a fairly reasonable used plane.
Fixed costs might be
£2k-4k on the Annual (depending on "suprises")
£1k-2k insurance
Variable costs might be
£50-100/hr fuel and the fund for the engine overhaul and the 50hr checks
There is a pile of other costs, to do with licenses, medicals, various unscheduled maintenance related stuff.
You need to fly some 20-30hrs/year just to stay any good. That will be the biggest ongoing cost.
More basically, flying is a game in which you need decent funding just in case something goes wrong. You need to be able to write a cheque for say £10k-20k anytime. Not saying you will have to but the capability has to be there. So if you have £50k don't buy a plane for £50k. Buy one for £30k.
You will get loads of feedback, with plenty suggesting you buy a microlight which you can fly for £0.10/hour
But there is truth in this - there are a lot of very cheap planes around now; limited to VFR only and frankly looking a bit flimsy (I saw some new 450kg ones from Slovenia at a fly-in in Greece last week) but they will get you, your Size 8 girlfriend and a toothbrush up into the sky for a lot less that you would expect.