how to price commercial music?

[ugo]

hi folks,
i need some pricing advice from the pros here.

our business is going to be putting togehter a 25-30 minute dvd presentation for a client. the video is to recruit college students to work for the company. the presentation will consist almost exclusively of interviews/monologues done by executives and other employees.

however, the job will need intro/outro instrumental music and background stuff. how much has not been determined yet (nor has style). its one of those 'we'll need it where we need it, but not where we dont...and we wont really know until we edit' type of situations. but we still need to give them a price estimate.

i've done very little commercial music work (usually just for flash site intros) and im never sure how to properly price. but im especially perplexed when the requirements/length/number of pieces/etc. are still pretty unknown.

should this be hourly or fixed price for the job?
if its hourly, how many hours would typically be estimated for a job of this type?
if its a fixed price, what are the going rates in the US for this type of thing?

thanks for the help,
-ugo