There's a scene we're shooting tomorrow that had an eyeball in it. I debated if I really needed it, since it was only there as a bit of a joke. In the end I decided I needed something, so if I could make a fast cheap eyeball - an eyeball it would be.
This was made from stuff I had lying around and pretty much anyone could make from stuff bought at any craft store. I already had a bag of styrofoam balls, might not be the perfect size, but they're pretty damned close so I went with them. I had some thick twine, the kind that's all splintered looking and rough. And a few paints and latex. And a tack and some hot glue.
Now this doesn't result in a perfect up close quality eyeball - but a nice cheap gag eyeball.
First I painted on the iris, didn't bother with anything else, just that. You could do more detailing if you wanted, but from the viewing distance and amount of time it'll be onscreen - it didn't matter to me.
Then I tied the end of the twine in a small knot and trimmed off the excess, stuck a flat tack into it and hot glued it in there. The resulting "optic nerve" was a little off centre, which was fine because I want the iris to be visible and it wouldn't have been so much had the twine run perfectly straight from the back.
Once the glue was dry I tied another knot on the other end, coated the twine in red tinted latex and let it cure. i made sure to make it nice and lumpy on the back of the eye and added some somewhat veiny bits. And that was it.
If you had the time, you could make a shitload of these for under $10 if you already own a glue gun and paints. And I suppose not everyone has access to latex, but I would think any glue that dries flexible would do it.
The reason I went with the twine was because I wanted the nerve to be thick and it helped create a lumpy, kind of ropey looking nerve.
Took very little effort and it yielded a nice campy looking eyeball prop. All the while I was making this I kept thinking of this scene from Blade Runner: