Standard rate here is $17 per half hour (my daughter tool lessons last year for a couple months), I am paying $25 for 45 minutes at present.
I know I can teach because 2 of my previous daycare children learned the basics from me.. but I only showed them a little at a time, as I am paid to provide daycare not give lessons. I had one girl finish Thompson's primer in about 3 months. She was VERY smart though... and I would show her a little, play the song for her, and she would do the rest... not formal lessons.
I offered free lessons to my Neighbor because they are always doing things for us, but the wont hear of it... said.. name a price... You are at home, your time is valuable... SO I can haggle them down a bit... I had to haggle them down on what the pay me to take care of their infant. They wanted to pay me what they would pay a daycare center, not what my going rate was... and I cant have them pay me more than I would charge someone else!!!
I would guess $5 for a half hour would be fair then.