I went with the low/middle of the road for my tripod (manfrotto) that I really like for the money; I think it was like $120. Personally, I really like the flip-lock legs, it's just so convenient. Of course, I really do want a nicer setup if I get more serious. I do agree, this is one of the most essential pieces not to skimp on.
I didn't put enough thought into a nice ballhead, mines only OK. It' doesn't have a really positive lock on it, meaning I have to really torque it when I have a heavy lens. It's rated for enough weight (supposedly), but I think it struggles with my big glass.
I love my monopod, but nothing replaces the tripod. I shot the Teva Mtn. Games and the monopod was perfect for that. I was able to get at an awkwardly low angle and keep it stable.