I started taking Guitar Lessons, when I was 14, from a personal instructor back in 1994 for 12 dollars per hour. Now in 2008, that same instructor provides lessons for 24 dollars per hour. When I first began I would see him once a week for an hour after school. He would give me a book to follow along and practice. And after that he would take a piece of popular music, he would listen to it, and write it down for you so you can play it the same way. He was quite talented.
References :

It varies on the teacher and your area of residence, but normally about $20 an hour (A lot of people charge more though), and depending on the teacher’s work schedule (And how many people he/she is already teaching), you can learn the guitar at any time.

And also, your teacher is going to request you buy a lesson book from a local music store (Or sell one to you) so you are able to practice at home between lessons. Books will cost anywhere from $20-$50.

Good luck on your guitar playing!
References :
4.5 years of lessons.

The price of lessons varies from teacher to teacher. When I give lessons, I charge $25 an hour. No books are required, however they don’t hurt. The only thing your required to have is a guitar of your own so you can practice at home. I have chord charts written out on index cards, which I provide at no extra charge. I give the chords that I want the student to learn and practice between lessons. Lessons are typically once a week. This gives the student time to really learn the previous lesson and memorize the chords. My current student is a very fast learner and has picked up on playing very quickly. He was also a beginner, and after his 4th week, he’s already working on chord progressions and songs. How quickly you learn depends totally on how dedicated you are.
References :
musician

Where I live, once a week, $15 for half-an-hour. Other places are more expensive.
References :