The choices depend on if the new bike is 9 or 10 speed. If 9 speed, a mtn bike cassette and RD and maybe a chain will work.That will cost about $100. For 10 speed, Harris has 11-32 cassettes but they are expensive and you will also need RD and chain. I expect the new bike will be a triple and you might try replacing the 30t small ring with a 26. In my experience this works better on some bikes than others and you may have to experiment. This is the cheapest solution, $20 for the chainring and $10 for a chain catcher if needed.