I believe the O Frame uses a lexicon lens and don't think Oakley offers replacement Ski lenses for that frame since its currently a MX specific goggle.
Using these goggles for skiing wouldn't work out well for you because they would continuously fog up due to the one lens design.
You should check out a local Vault and try and score a decent pair of A Frames for $80 or an older lexicon lens based goggle for around $40 if you're lucky.
After doing some experimenting, you can indeed interchange MX and snow O Frame lenses. Looks like the only lens on the main site is fire, but it's a pretty good all-around lens so that should work: Oakley O Frame Snow Accessory Lenses | Official Oakley Store
@Holbrook Henderson I think the word you're looking for is Lexan. Lexan sacrifices a bit of impact resistance and does have a bit of optical distortion (not to where you'd really notice, just because it is not a spherical lens shape), but it is significantly cheaper.