I also have two eyes that take radically different prescriptions. I have bifocals and using them for modeling is not ideal.
I tried some high diopter (high magnification) reading glasses, and lo and behold, they work fine! I assume that with enough diopters I still have enough accomodation to even out the differences in the eyes.
Go to a drug store or discount store and go to the rack of reading glasses. Take along a card or something with fine print, and try several pairs of reading glasses, with the card held at a comfortable working distance, till you find something that works. I find about 1.5 to 2.0 diopters works for me, but you need to experiment. Dollar stores sometimes have them too, at cheap prices.
I find strong reading glasses almost as good as an optivisor or similar, but at much cheaper prices. In fact, I have been thinking, at my next eye exam, to get the optometrist to give me a prescription for a close working distance. I suspect single vision closeup glasses will be as cheap as an optivisor and more comfortable to wear.
One time I also optimized a set of reading glasses by buying two sets- one optimum for my left eye, on for the right. I picked ones with the same frames, so I could use the one eye's lenses from one in the other frame. But, as I say, when I went to even higher power, the eye accomodation seemed to take over and work okay without all that trouble.