To just become an instructor, I'd say it's not quite as bad as Jock suggests:
PPL - £8k
Hour build - £15k
CPL writtens - £2k
Instructor course - £6k
Medical - £500
£32k or so.
If you want to be a microlight instructor only cheaper still:
PPL - £5k
Hour build - £10k
Instructor course - £4k
"Medical" - £10.
£19k or so, and it pays better as well, plus provides good opportunities to start your own business that are less there in the light aircraft world although realistically at-least £10k investment in an aeroplane and a few other oddments is going to be needed to do that.
G
N.B.
Typical flying school light aeroplane (typically 30+ years old)
Typical microlight school 3-axis aeroplane (typically less than 10 years old)
As you can see, you're quite right and microlights are much cruder still
