I would love to purchase a Nikkor PC-E Micro lens for product photography, but unless I win the lottery, that ain’t gonna happen. The more product photography I do the more I realize how much I enjoy it and how profitable it MIGHT be. That is a MIGHT since I am still focusing (pun intended) on school (@NYIP). Anyway, while researching the issue of limited DOF in table top product photography, I have read about Focus Stacking in Gimp as well as using tilt-shift lenses. Both solution can offer sharper images where traditionally DOF has been limited.
This article by Henk van Mierlo on the Nikon Rumors site has me eye-balling the Nikon PB-4 bellows as a possible, affordable, solution.