Least expensive and simple would be to install a mountain crankset. Going as low as a 22 small ring would make it a billy goat. Should be able to find an LX Shimano crank for $150 or less. The swap is simple and the only other thing needed would be to shorten your chain.
You could go with a mountain Derailleur and cassette as well but.... I would go with the crank first and see if you really need lower gearing after trying the mountain crank.
my 2 cents...