My wife & I have taught guitar/banjo/recorder on and off for many years, mainly to younger pupils, but with the occasional adult. Cost? about £10 - £15 per half hour session, which is usually enough for most youngsters.
The most significant thing which we have learned is that its important that the pupil wants to learn the instrument as we have had several instances where the parents think "It would be nice for ?? to play an instrument"
Most of the good ones have become friends who we never charge .
I echo the sentiment that someone who already knows a few chords would be better of teaching themselves. I am somewhat proud of the fact that I never had lessons (couldn't afford them) and learnt from watching & listening and buying a book called -every guitar chord ever known (I think thats it title but its now out of print.
Good luck and keep on playing -thats the important thing