Okay, here it goes.
270winchester vs 270WSM.
-The case of the 270WSM is fatter. This means two things, the magazine will hold one less round, maybe two.
-The distance you have to pull the bolt back will be 1/4th an inch less, which might be a tiny tiny bit faster for some people.
-most 270s are in 22 inch barrels, most 270WSM use 24 inch barrels
The actual bullet (the lead projectile) for these two is exactly the same. However, the WSM pushes it's bullet a bit faster. The extra 2 inches of barrel helps out for faster speed too
federal ammo data
However, it only pushes it a little bit faster. What this means is that not a lot of hunters think it is enough different to bother buying onr. Plus, it has only been around for a short time. That means right now, you walk into a gunstore, they will have a very limited selection of 270WSM loads but a TON of 270 loads, and probably only 1 rifle for every 10 regular 270 rifles.
This also means your ammo will cost more money.
This also means your gun will probably cost a tad more.
This also means you have less chance of getting a good used gun.
This also means by the time you are 25, they might have stopped making 270WSM loading.
Now, for the biggest game, both 270 and 270WSM can take elk, but that is really pushing it. As always, the shooter matters most, and many elk have been taken by 270, so 270WSM would work just fine too. Neither one would be my first choice for an 'elk only' rifle, but 270 and 270WSM make good pronghorn+deer+carbou+bighornsheep+elk 30-06 covers the same range, probably covers the elk end a bit better, while the 270 covers the pronghorn end a bit better.
270 and 270WSM are lacking for grizzly bear.
Regarding 'what rifle' for your price limit, I'd say a savage will do you well. It will be available in 270, 270WSM, plus 30 other rifle chamberings. Remember, the 270SWM is a 'short action' and the 270 is a 'normal' or 'long' action.
http://www.savagearms.com/11f.htm -short action 270WSM plus others
http://www.savagearms.com/111f.htm -long action 270 plus others
Note: the 270WSM has a 2 shot magazine, the 270 has a 4 shot. I'd take 5 shots in a gun over 3 shots, even if the 270WSM shoots a little bit faster.
Also remember, the listed suggested retail price is more than you will be charged. Expect to pay about 10-20% less.
You asked about the 243. As you can see, it is another chambering you can get for the 11F. It is smaller and lighter than the 270WSM. It is more suited to game up to deer size, NOT for elk etc, but works great on deer. While it is less common than the 270, it is still VERY common, you won't have any trouble finding 243 ammo for years to come, plenty of rifles in it too
the 25-06 and the 7mm-06 are also excellent deer loads to consider, but seriuosly, get the 270 and you will be happy even when you are 70 years old
!