Well, if I wouldn't have to travel to your place, and would be your hardware, I'd do it for $75 Resume: Helped a friend cut Cristina's lawn in El Calafate back in the 90's
I agree that a higher price would be ok depending on variables as teacher experience, offer/demand for the specific language, materials, travel, tax, etc. For an informal class where the teacher doesn't even have to move from his place, I think a base $70 to $100 depending on experience and moving on up with inflation from now on is ok.
My girl paid $100 for hour and a half Spanish lessons off a High School literature teacher few months ago. Don't think it's so crazy, you'd be earning at least double p/hour over a full time high school teacher where you have to go to meetings, correct homework, deal with brats, etc.
Last photographer gig I did (I have a degree in audiovisual design but I'm not a full time photographer) back in July charged $300 for 4 hours and included the trip to the bar, and I'm going with a U$2k equipment. I'd probably charge $400 now because would have to raise the insurance as well.