Based on all I have read, it is much more cost effective to get a good tripod/head combination at very first shot. Guesstimate what will be the heaviest lens you may purchase later and then get a system that could support that.
I tried my colleague's $90 Sony tripod once and a slight wind blow will shake my D80 + 70-300 VR (a very light lens). So, I will not buy "cheap" tripods.
I would wait until I could afford a decent one.