That kit includes the nuts and bolts. You can buy them from the dealership, but you're looking at $5 per nut/bolt. Yeah, the polys are pretty spendy compared to the rubber alternatives, but I've heard the rubber can wear out pretty quickly, whereas the polys are for life. Maybe your mechanic can get the nuts and bolts for cheaper?
Replacing the bushings on just the lowers will fix the sway in a big way, but if the lowers are degraded, the uppers are likely to be as well. If money's an issue you could always do the uppers later. A number of folks here have only done the lowers and have no complaints. I prefer the peace of mind and just did all of them at once.
I have no idea what labor would be like, but I would throw out a guess of 2-3 hours a set at the standard rate of $100 an hour. If you want to shop it around a bit to get a better idea, I do actually know two great shops in SoCal.
Marlen Motors in Monrovia and Scott's in Rancho Cucamonga (10013 8th St # E2) both do top-notch work. If you were up here, I'd say bring over some beers one weekend and we can do it ourselves
I don't know how much of a safety hazard it would to leave them as-is, but I would highly recommend addressing them in some capacity.