Ok, this is the deal. UV LED emitters are pretty crappy from a technology point of view. You've got:
a) The 5mm ones. These are basically like the lame 5mm LEDS in the showerhead looking lights. Being UV, they are significantly less efficient. We are talking 20 millwatts of power each.
b) The CREE power LEDS. These have a few WATTS of power each, but are HARD TO FIND. CREE discontinued these a while back, so they are way behind in tech. But certainly beter than (a). This is your best bet but expensive due to rarity.
c) Flourescent. If size isnt an issue, get a 8 inch TUBE LIGHT. I have one and it produces TWELVE WATTS of power! Thats a crapload of UV, compared to LED offerings! And it was under 20 bucks. 8 inch tube light with multiple AA batteries running it.
Remember that UV is not the same. You want about 380 nm wavelenght. Many cheaper LEDS produce much higher wavelenghts and you see lots of PURPLE LIGHT but not so much UV. The Tubes (c) produce the correct wavelength.