If you have a bolt action rifle the amount of time you'll spend in brass prep is going to really tick you off, but if you get it to shoot well in your rifle it will last a pretty long time with good care.
If however you have a gas gun that is really hard on your new brass and are willing to take the steps then once fired GI brass can be a good option pricewise.
I've loaded a lot of once fired M80 ball brass, it involves cleaning, depriming, decrimping, annealing, resizing, trimming, chamfering, and that is just to get 4 reloads out of it (the rule is 4 reloads and chuck it for most semi auto rifles). I happened to get a bunch of it in trade a long time ago, and if you have a lot of spare time (like I did back then) it can be worth doing.
If you buy from someone who will process the crimp out for you like Jeff Bartlett of gibrass.com I would recommend it. I visited Mr. Bartlett at his warehouse in Owensboro KY and purchased 2,000 once fired 5.56 brass that he had processed for 20 bucks per thousand. Saved me the trouble of cleaning, depriming, and decrimping. Well worth it in my book. I don't hesitate to recommend gibrass.com as I have been very happy with my purchase.
If you can get once fired M118 brass it is usually worth the extra money as it is usually fired from sniper rifles instead of being run through M240 machine guns.
Machine guns are awesome until you have to carry one.