Use priceline.com for cheap hotels. Looks like the show is on a wednesday, that's good, midweek you can get something good in midtown in the $120-150 range. Standard rack rates on websites will be in the $250-300 range. In NYC it doesnt really matter where you stay in the city anymore, everywhere in manhatten is equally convenient and safe for sightseeing.
For dinner, you might want to look into restaurants with prix-fixe (pronounced pre-fix) menues. They are quick dinners that start at about 5:30, and they are on top of their game to get you out to your theater show since most start at 8pm. Not sure when the concert starts, but they should be able to accomodate you.
If you're staying an extra day or two, and feel like walking over the brooklyn bridge, take the subway to Grimaldi's in brooklyn, eat the best pizza you'll ever have in your life, then walk back over into manhattan.
http://www.grimaldis.com/brooklyn.htm
Enjoy man.