Seattle Forrest

You could spend a whole lot of money changing your gearing to make it a little easier to climb hills. You'll still have to do the work of getting yourself to the top, you'll just have an easier gear to do it in. Going to a triple would be cheaper for you than for most people, because you can use the shifter you already have, but it still won't be anything you'd mistake for free! It's less expensive to change your cassette, like you're thinking about, if your RD can handle that many teeth.

Or ... you could do hill repeats, and maybe throw in some diet. These will also make it easier to climb the hill, they'll take longer but be a lot more pronounced, and they won't cost you a cent.