Hi,
I think that I am going to disagree with a lot of people on this forum. You should damn well charge for your time and experience. They are worth something to you. Also, odd as this may sound, people tend to more appreciative of things that they spend their money on, provided that they get VALUE for their money.
How do you think Bennedetto charges $40k for a guitar? They use pretty much the same materials as everybody else, they just do it really, really, well. Just like your first guitar. Or was your first guitar a fluke and not representative of the real quality of your work?
Don't take this to mean that you could, or should, charge $40k. But how many hours went into that first guitar? By this I mean real working hours, not learning hours. How much do you make at your regular job? Multiply those two numbers, and you know what your time is worth to you, swapping one job for the other. Now you can adjust the fee according to your requirements and your friends desire for a guitar.
One other word of advice: Contracts. Use one. Who owes what and when.
Guitar Ed
Yes, I am an @sshole on occasion