It all depends on how much you will shoot. $3 per shot isn't bad if you only shoot 20 per year. But if you shoot 500 rounds per year it adds up in a hurry! All premium ammo is fairly spendy, but it is more so for the magnum cals.
Britz is right, and once you start shooting long range you will more than likely get addicted to it, which means you will be shooting alot. We shoot about 50-100 rounds every month when we get together, that's 100 in one day, I don't think you would be very happy with a magnum after that.
There is a F-Class shoot once a month in New Braunfels at Central Texas Silouhette Association - CTSA (about 30 miles from you) that I go to, it's fun and you can learn more in a couple of matches there than you can learn in about 2-3 months on your own, and by the way, you will meet many friendly and knowledgeble guys there. The first time I went there I just wanted to watch, they asked if I brought a rifle and I said no, before I knew it they had me shooting 550 yard match behind a full custom .223, after that, I was hooked!
I still say stay away from magnums at this point. If you happen to like F-Class you can shoot in F-TR which means you will be competing against 308 and 223, if you have a magnum, you will be placed in open class, which can be very humblling experience, specially because you will be competing against 6.5-47 Lapua's, 6 Dashers, 6BRX's, 260's, and of course the 6.5-284 Norma's.
If you get a 308, I am set up to reload for 308. You can come over one day and I will walk you through the reloading process and help you work up loads for your rifle, then you can load up 100 or so rounds in about an hour or two with my equipment and have enough to practice with for at least a month. I have done this for a few of my friends before they could save up enough to buy their own reloading equipment and learned enough to know what equipment they wanted.
Hope this helps.
-X3M