I am familiar with the standard lens/filter system often used - the UV-Nikkor 105mm f/4.5s lens, what I am wondering is if there are cheaper alternatives to this standard (which I believe is also discontinued?). Is it possible to be able to obtain such equipment for less than say US $500?
The problem with UV photography is that standard optical glass filters out UV light, so lens designers have to turn to more exotic formulations such as phosphate glass, or other materials such as quartz. This fact combined with the very low production volumes are not a good recipe for cheap lenses.
I can't answer with a hundred percent certainty, but the only UV lens I know of in production is the Coastal Optics UV/vis/IR 60mm macro lens which sells new for $4500, and the only other lenses I know of in the used market were by Zeiss and Rodenstock. And I'm afraid you don't often hear the phrase "rare Zeiss lens" or "rare Rodenstock lens" in the same sentance as "under $500"...
You can rent the Coastal Optics UV-vis-IR lens from lensrentals.com for three weeks for $531
You can use EL-Nikkor lenses (can be had quite cheaply on eBay) for UV photography.
Hope it is okay if I plug my own site here, as I recently wrote a guide about the equipment and technique I use for UV / multispectral photography: Vis UV IR flower photography guide.
Also check out Dr. Klaus Schmitt's Photography of the invisible world website for more info on UV photography (including using cheaper non-quartz lenses).
Yes, certainly there are quite a few capable lenses for UV work without having to spend $$$$. I have done research on that for years, which may be found on my BLOG uvir.eu and there is a thread summarizing it here: http://photographyoftheinvisibleworld.blogspot.com/2011/01/uv-lenses-tested-good-for-uv.html some of them reaching down to 320nm, more than sufficient for UV flower work as UV nectar patterns usually get visible between 350-380nm.