Keep in mind that I haven't been out there yet, but I based my selection on several goggle threads around this forum.
I wear prescription glasses. Doesn't seem like a good idea to wear contacts in a dusty situation.
My main daytime glasses will be these: http://www.riderseye.com/ItemDetail.asp ... n&Style=82
The foam eyecup is removable, so they can be regular sunglasses or motorcycle sunglasses. The strap can be attached and it will pull them tighter so they're more like goggles. My configuration and prescription ended up at $87 shipped.
Next, I have these: http://www.cheaperthandirt.com/product/MIL-1128
They can be worn over glasses, and have a clear and a smoked lens. 10 bucks.
Finally, I have some cheap prescription glasses so I can leave the expensive ones at home. They cost me $27 including shipping and upgrades to anti-scratch, anti-glare, and polycarbonate. EyeBuyDirect.com for the deal.
So...I can wear the motorcycle glasses as dust resistant glasses or goggles. I can wear the bigger dust goggles over them with the clear lens, if needed for extra dust protection. I can wear just the regular glasses, glasses plus dust goggles in the dark, or glasses plus dust goggles and smoked lens in the sun.
I figure that will cover all the bases for eye protection from both dust and sun and crappy eyesight, for about $125.
Also, a shemagh for breathing and other protection.