How cheap can you be?
When I instructed in the UK I got £20 per flying hour. My total round trip mileage was 214 miles per day. Working on an average of 3 hours flying per day there's not much left for food is there!
Please also remember there's quite a lot more that goes into a lesson than just the time in the air. There is all the briefings and de-briefings, all the standing around while you take a million years to pre-flight the aircraft and even longer to get the thing started, then the time wasted going back to the clubhouse because you forgot your headset or the extra hour waiting for you because you didn't come prepared. The list goes on and on!
If anything I believe instructors should get way more than they do! Stop complaining about paying dual rates when solo, this adds up to a maximum of £250 over the whole PPL cheapskate!