Since Glasgow is not on Rick's Scotland tour, and is an easy, one-hour train ride from Edinburgh, you could spend a couple of days there between tours. You can fly from either Edinburgh or Glasgow to Dublin on Ryan Air for about $20 plus fees (follow all their rules carefully) or Aer Lingus prices start at $40; see www.skyscanner.com for these and other options. The order of visiting should not make much difference, but if you think that Ireland sounds slightly more "exotic," then I'd see it second.
Despite these cheap flights, you can avoid back-tracking if you book your trans-Atlantic flights as a "multi-city" trip, such as into Edinburgh (or London, if you plan another stop before the tour) and out from Dublin. London to Edinburgh is only a 5-hour train ride, but it's expensive, unless you book nonrefundable tickets a couple of months in advance.