visit gobycoach.com for timetables and prices. not surprisingly, Leeds (main bus station) is the nearest National Express hub to the Uni. You'll probably need to get a further bus or taxi from there. Alternatively, consider the train, in which case you could get a connecting train to/from Burley Park or Headingley.
IMHO you'd be better getting the bus to Uni. Of Leeds as the bus and train station aren't in the same building, (and it's perfectly accessible by bus) but if you're going to Leeds Met then it's only a short walk from the bus station.