I agree that killing a cow is K utils no matter who does it, but eating a cow is E_me utils if I do it and E_other utils if a stranger does it. If E_me > K > E_other, then my utility function supports paying for other people to not eat meat.
If E_me > -K, your utility function supports you eating meat, regardless of whether or not you are able to pay someone else to go veg. If E_me < -K then your utility function supports not eating meat, once again regardless of whether or not you can pay someone else to go veg. (Also you forgot a negative sign).
You wouldn't pay someone else to not eat meat unless that was the most utility generating thing you could do with your money. If your E_me > K and you would pay someone to go vegetarian, it means you are part of that "very small set" who values animals more than all other causes you might donate to while still not valuing them more than eating meat.
I notice that a large fraction of Effective Altruism people are vegetarian. This makes sense: in general Effective Altruists take moral issues seriously, even when that means changing your lifestyle. I'm not sure it's a good balance, though.
One way to think about this is to convert it into money. How much would I need to be paid to give up eating meat? All animal products? How much money would I need to spend on myself to be about as happy as I would be with less money but continuing to eat animals? I'd probably be willing to go vegetarian for about $500/year, vegan for maybe $2000/year.
It turns out you can probably pay to convince other people to be vegetarian much more cheaply than that. I estimate the cost of a vegetarian-year at $4.29 to $536 while Brian Tomasik estimates $11 with better methodology (which I looked at). This is by placing ads on facebook for a site where people can watch an animial cruelty video and ideally become vegetarian or vegan.
If you would get more than $11/year worth of enjoyment out of continuing to eat meat, why not give $11/year to convince someone else to not eat meat for you? Or give $50/year and be on the safe side?
(While you're giving money, you should probably give it to the organization that you think will do the most good with it, which I think is probably one of GiveWell's top charities. The nice thing about money as opposed to actions is that it's easy to redirect.)
I also posted this on my blog.