I usually order from
Reptile Supply. They are very competitively priced and they have the TRex 100w flood for $48. I've been leaning towards the ZooMed Powersun 100w floods which are only $39. They don't give off as much UV as the TRex bulbs, but then again, I think the RES doesn't really need that strong a UV output to be healthy. I may be wrong though. My feeling is that if people have been successfully raising RES with only flourescent UV bulbs for so long, then the ZooMed MVB is still a major step up, and costs less than the TRex bulb. Also, the very high UV output can be damaging to the eyes and it sounds like RES may be susceptible to that.
Either way, do not place any MVB bulb closer than 12 inches from the surface of your turtle. If your turtle is small and/or the tank is small (say less than 40 or 50gal) you may want to keep it higher, like around 15 inches or more. The MVB bulbs are good at generating UV up to several feet away. Make sure to check the basking spot temperature under the bulb carefully so you don't burn your turtle.