For the longest time I just wore a pair of cheapo amber-tinted air-soft glasses .
One of my best friends that just finished 4 years in the 82nd gave me a 3 piece lens set of ballistic Oakley safety glasses, along with a bunch of other neat stuff. He said it was payback for the frequent care packages I sent him during his multiple tours in the sandbox...I laughed at him and told him my care packages weren't even close to enough payment for his service, but I was grateful anyway.
I would think that anything type of (somewhat sturdy) plastic that covers your eyes and the surrounding area will suffice. If you have a KB or the likes and it is enough to break the plastic, you have more worries than just damaged eyes.