I have a hardrock (03-04 model) and would recomend one to someone on a budget. I believe I paid around 500 but the wheels were crap. Luckily I had a replacement pair already. I cant find anything wrong with it (asside from the wheels).
Lock out on suspension is not needed, especially if you are on a budget. I loaded up my hardrock with a rear rack and panniers and was amazed at how little suspension movement there was. With the Bob trailer you will not want to swing the bike back and forth, so keeping a silent upper body will prevent suspension movement as well.
I would set asside money for the possibility of a suspension seat post, as I hear there are sections that are quite brutal on the butt.
Scott