You don't need a lawyer, just some money.
http://soundexchange.com/rates.html
$0.000762 or 1.17 cents a tuning hour.
Hmmm, well it's gonna be a lot easier to figure it out on a time basis. You do have to do some primitive reporting (to the best of your capacity), so it's easier to give the an hour count than a song count.
One way you can save a few bucks is by only using ONE of ascap, bmi or sesac. You'll have to sort your music. BMI seemed to have the best rock catalog.
It is best that you get a pencil and really figure out what it costs.
And then pay the money....