I used to find that the cheapest way to fly was to get three friends, fly somewhere interesting and split the costs with them.
Not surprisingly I used to find that if I asked my friends to come flying with me, maybe to another airfield for a cup of tea and pay their share of the aircraft hire cost, they usually told me to sod off. If on the other hand I suggested paying 25% of the cost of a trip to France for lunch, I was generally swamped with volunteers and found that I could manage a French trip just about every weekend that the weather permitted.
From round here to France takes about an hour each way. So two hours at £110 ish an hour, less the fuel drawback (do we all know about fuel drawback?) split four ways was about £50 each. That's £25 an hour. Flying doesn't get much cheaper than that and done the way I have just described - cost sharing for a PPL holder is absolutely legal.