You're either being taken advantage of or this musician isn't quite up-to-speed on this kind of work.I have been a professional musician and have done tons of theatre gigs. Yes, there should have been a contract, but I would never have gone into a gig not knowing what I was getting paid. So, that is on your musician, as well. Also, I was almost always paid a flat fee per evening of work.Most importantly (I think, and what makes me think you're being taken advantage of), a professional or semi-professional musician should never charge for their home practice time. I might ask to be reimbursed if I had to rent a specialty instrument for the job (alto flute, etc), but then it'd only be the cost of the instrument's usage, but other than that, I can't think of any other charges beyond the evening's work. I have had to walk in an hour before a show and read it during a performance. This is no accounting for practice time in that situation, you just have to be able to do it. If he couldn't, that's on him...I'm finding the more I type, the more irritated I am at your musician...For reference, when I need a solid guitarist for a show, I pay my guy $300 for the 3 nights of the show plus 2-3 rehearsals. It might work out to $20 an hour, but that's just for time playing. It's not as much as I'd like to pay, but I know it's relatively comparable for this kind of work in my area.Also, if you want to put things in perspective, the current base rate for a Broadway musician is about $222 per evening. I don't know what your guy is asking, but it sounds like a lot. Especially in comparison to your budget.
Let's look at the elephant in the room. The big issue is not what your musician is paid for a show, the big issue is why are Drama teachers given so little a budget for directing a show at a school that a musician's wage is 1/4 the whole budget.
Doing the math – the rehearsal and performance times you mentioned, plus I'm adding an arbitrary 10 hours of personal rehearsal and preparation (sounds like he's a guy who takes his worth seriously), I'd guess he's billed you around $1500 - $2000? That doesn't seem like an unreasonable wage to me (for what is about a 2 week time period, where he can't take on any other gigs). But what is unreasonable is your pay. And why is your music director being paid so little. And why is your budget so low. Yes, it's the same in most schools, but why, when a cross country team (for instance) can hire a running coach, a jumping coach, a pole vault coach, a hurdles coach, even someone to be a timer, or a football team can hire a kicking coach, a running coach, a catching coach, a throwing coach, ticket takers, the list goes on and on, each at about $2000 per season – why then can we not hire a singing coach, a band coach, music support, a lighting coach, a set coach, a sound coach and so on?
This is a systemic problem at high schools in our country, which we all buy into. One person mentioned "its just simply not how things are done realistically, especially at a school", but does it have to continue to be that way? Should it be? When you go to your principal (when we all go to our principals), perhaps the conversation to have is how many students are 'served' by putting on a play (more than any sports team), how long the rehearsal process is (as long as some sports 'seasons'), how many "coaches" it takes to serve/supervise/mentor/train the students and how many hours they put in. I know, all administrators say they don't have money, but they do, they just don't have an understanding of the value of what we do. It's up to us, collectively, to take the elephant to the principal's office and have the conversation; not to lower someone's wages to fit within our budget, but to raise our budgets to a reasonable share of the principal's budget, so that we can properly support the education of our students.