Been quite busy lately work and off work (research ofcourse primarily in urlrewriting) but I couldn't help but notice and comment on a post from CodingHorror/Jeff Atwood on this topic [more]
I could very much relate to this (not to mention that somehow I'm particular about productivity and ergonomics). Though don't get me wrong I can't afford 500$ chairs I do value ergonomics or at least in a simple way my comfort most especially those involving work. I have a Php 3000 Logitech MX 610 wireless mouse I'm comfortable with, fits my hand/palm well with curves and a bit inclined rather forcing my wrist to twist flat on the table. I also have a sort of wrist gel for my mouse (don't cost much but what some may still consider unnecessary). I also think of getting a track ball mouse from time to time and will probably happen soon. There not much chair options here as I've gone to the malls or furniture shops but I'll probably save to get a better chair soon.
Ergonomics is not really something popular here in the Philippines (was looking for a good ergonomic keyboard before and all I can find is the common "A" shaped one – that's how ergonomic it can go here) but I hope it changes soon.
Comfort is subjective but be sure that you are not depriving yourself of it just because of the price. It does bring productivity or even just lessen worries/irritation and focus more on work. Not to mention that health is priceless. 🙂