I've purchased a few Drum Corps Brass Scores over the years. I get them in their original Bugle Score form (from corps like BD, Madison and Phantom) and they usually range from between $100 - $250 each for just the Brass Scores, depending on their length and complexity . . . and also the arranger - some are more humble, while others know they are good and their prices are reflective of that).
If you want the Corps Arrangers to do an original arrangement for you, it can run around $750 on average for just a Brass Score, and if it's a really complex arrangement, the sky's the limit.
Regarding Percussion Arrangements, I read the following post by Don Click regarding his philosophy (I hope he doesn't mind me quoting him . . . my apologies if he does):
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I write a lot of fall and winter music, and have a "general" guideline I use:
Pit OR battery only: $175 per minute
BOTH pit and battery: $300 per minute
Show design: Quoted Per
I take into consideration MANY things though....if I have to come up with the concept and basically block the show, I'll charge more. If the band has NO money, but I would still like to write for them, I charge less.
I also use this when determining fees:
Band Director can choose ONLY 2 from the below 3 choices:
1. What I write is GOOD
2. I write it FAST
3. It's CHEAP
So....if they want it GOOD and FAST...it's not going to be cheap!
If they want it FAST and CHEAP...it's not going to be good!
If they want it GOOD and CHEAP...it's not going to be fast!
Don Click
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According to another post, Jim Casella (SCV) charges $400 per minute . . . so obviously it varies.
And that's coming from a well established Percussion Instructor / Arranger. I would assume that Brass Arrangers have a similar philosophy.
Hope that helps.