The cheapest option would be to get a new rear cassette for sure as others have pointed out. As for myself I ride a compact double (50/34) and 11-25 rear. I live in Northeast TN and I'm always climbing and the compact works very well for my area. I rarely feel I need anything lower than 50-11 but I have been thinking or getting a 12-27 or 12-28 for those epic climbs some rides. Before I got my new bike with a compact double I was worried 50-11 wasn't going to cut it but I was pleasantly surprised when it did. I wouldn't go back to a standard or even a triple now (unless I moved to flat lands but that's not happening). OP I would get a new rear first then if u feel u still need something more get the compact and then u have 2 rear cogs to switch out as the ride dictates.