UVEX also makes a prescription goggle:
http://ski-n-see.com/uvex.html. I'm note sure if it is available untinted.
Other options in the "UVEX" line of goggles would be their product code 4001012208 or 4001012248. Both are designed for spectacle wearers, have clear lenses, and are relatively inexpensive. See further
http://www.sunglassesetc.com/sportgoggles.cfm
Finally, "Flightsuits.com" in California offers the Type 521:
http://www.flightsuits.com/open_goggle.html
Please report back on how things work out!
P.S. Here is a short discussion regarding tints:
http://www.vnh.org/FSManual/09/08Eyewear.html