I would suggest that you do both lower arms (and on both sides). If it's been like that for a while it will have put undue stress on the other arm bushings. I did mine recently, not expensive on parts at all and as it's been suggested, a couple of hours to do but you absolutely MUST not tighten them until the car is back on the floor (or wheels at normal ride height at the very least) or the use will twist and start life under more stress than it should be which will result in it lasting about a 5 minutes and need to be done again. Most garages and mechanics know this is usual practice for any bushes but it can easily be forgotten.