For keeping the ammo cheap, the .243 is a good option that won't be "overkill" on yotes. That being said, I don't see anything wrong with making them extra dead.
The .308 and '06 options will also do fine with cheap ammo available and far more capability on the upper range if you ever want to take on larger game.
If spending a bit more on ammo is OK, then I would go with 7mm08. Extra punch available for the big critters, but without the recoil of the .30 cals. They do cost a bit more to feed, but a little looking around can score you some reasonable prices. I found some locally for $16.99/box. Not as low as others, but not too oppressively expensive, either.