Yeah, a dead moose with a caliber you dont approve of...
A 243 isnt a "best" option, but I'd much rather have a guy with a 243 he can use than half the guys on the site with super duper magnums that couldnt hit the broadside of the barn...
If a 243 is all you can afford, it will do the job... I've heard of guys on this site killing moose with 25-20's and I know an oldtimer that hunted moose with a 250-3000 model C for about 40 years. Other than a few thousands of an inch, whats the difference? Nothing. If your going to buy a rifle primarily for moose, and you havent spent your money yet, look at something a bit bigger. Maybe a 308? Is recoil an issue? If so, there are many options that will allow you to use a larger caliber with less felt recoil. Good pads, muzzlebreaks, mercury recoil reducers... lots of options...