Just joined what band? Who is saying there are all these expenses? Is this a school band and the music department is telling you this? Has he signed to a record label and some agent or manager is telling you this? Or is it a garage band with some buddies and one of the other kids is saying they need to do this? How old is your son? Information is a wonderful thing.
What's a reasonable cost depends on what you're talking about. Kids launching a garage band shouldn't be spending much of anything, just a facebook page and DIY promo, etc. Different studios have different price structures when it comes to recording an EP - some charge a flat rate per song, most charge an hourly or daily fee for the use of the facility, etc. If this is a record label launching a huge campaign to get your son's band on the radio, on the other hand, yeah, it will cost a lot. My understanding there is that they usually pay for it up front but then the band owes it back, normally out of whatever money they make (e.g. if the label spends $10,000 promoting a song and the song makes $10,000, the band gets nothing; if the song makes $20,000 the band gets $10,000, if it only makes $5K the band is $5K in debt).
As far as tax deductions go, ask a tax professional, but I believe the rule of thumb is that business expenses are deductible, so if the band is a business, yes.