If you have the time, a slighter larger budget, and they're good enough friends surprise them with at road trip to see one of their favorite bands. If they're as big a fan as you say then there should be plenty of possible gigs and you can choose from here, Philly, NYC, and still be able to drive, but there are also cheap flights to boston, buffalo (Toronto), Norfolk. I've done this a couple of times, and if you're able to really keep it a surprise, probably take a couple of white lies, it has gone down pretty well, and if you take a bullet (ie. take them to see someone they really like, but you think sucks) in the process it shows that you genuinely care that they are getting something special and not just taking them to a show you wanted to go to anyway.