This is wise. It's unrealistic for an indie movie production to think they'll get anything popular or well known. Try for someone up and coming, someone who needs a break. try to sell them on the notion that your movie will be the way they break into the industry. Also you could try some music major college students with lots of computer equipment and musical know-how to mock up an inexpensive score. Either that or go completely obscure and get atiquated music that you'll probably get for free. Also never underestimate the acoustic guitar. I've seen great films entirely tracked with acoustic songs by ONE guy. Be creative. Don't think you're gonna get anything pop and don't think it's going to work if you do, because nine times out of ten pop songs DON'T work in movies.
Realistically, I don't know how serious this production is and how big the viewing base will be. You could always just swipe the music and hope you never hear anything about it.
I also think it's pretty important for the writer of the scenes to have music in mind WHILE writing the scene! So, he can line up the lyrics, get the timing right and make sure it paces properly. I'm always affected when a piece of music moves with the scene. When the chorus hits at the right time or when the tempo picks up at the right point in the scene. I love that.