Surely the cheapest and most effective method would be to ask a friend to poke you in the eye before you shoot.
The cheapest way that I know of is to close the dominant eye, its painless, but does lead to a loss of binocular vision and therefore loss of distance perception.
Getting a mate to poke you in the eye is quite painfull, could lead to a distraction due to the pain, isn't really a repeatable fix, and still leads to a loss of binocular vision, and you'll owe your mate a favour!
I've only ever once seen a cross over stock, that was recently on an expensive gun for sale at Kelbrook. A cross over stock is a masterpiece of stock making, but is bespoke to the shooter.
Shooting off the corresponding master eye shoulder is probably the best solution, but it doesn't solve the problem if you are trying to shoot your dads gun, or you've been shooting for ages and your dominant eye changes due to age or stress. Learning to shoot off a different shoulder is doable, but not enjoyable.
I genuinely can't remember how long I've used a Uni Dot for, but it's well over a decade. I've recommended the Uni Dot to dozens of other shooters over the same period, as far as I'm aware they are all still utilising the sights and many have returned for additional sights for replacement guns, additional guns and friends.
A Uni Dot sight costs around half the price of a slab of cheapish cartridges, a small price to pay for a cleaver piece of technology that could easily save its purchase cost at the practice clay ground.
webber