A bit difficult to post without appearing to be soliciting for trade, but we charge way less than £100 (chock-to-chock) for a Warrior II plus instructor. No exam fees for the first attempt, no landing fees at base aerodrome, no headsets to pay for, no groundschool fees - but the downside is that our FIs are part-time volunteers, so booking lessons can sometimes present difficulties as it's a question of 'will there be someone available'.
The only way to keep costs low is to rely upon part-time volunteers who are happy to get some flying but don't rely on using it to pay their mortgage - just covering expenses and paying to take their other half out for dinner, perhaps. Regrettably it's a fact of modern life that there aren't many people who are able to give up their spare time to instruct because of pressures on their 'day job' and the ever-increasing (thank you, JAA...) cost of maintaining licence and rating. Having to pay £150+ every 6 months for our Class 1 medical being a case in point...
I have part-time FIs from a variety of backgrounds - a bank manager, engineer, airline pilots both active and retired, military pilots both active and retired, an airline purser, an automotive engineer, an IT software engineeer - all sorts of folk. But if I had to set up 'commercially' with 4 a/c and some full-time FIs, I'd be charging the same as every other school, I guess. We're non-profit making, so 'The Management' (me) don't add their profit element - which helps!
There's a reasonable chance that the impetus of the NPPL may precipitate changes in the whole PPL training world. The experienced part-time PPL/FI might reappear again in larger numbers. That should help to make PPL flying more affordable, with luck!