Free: Contests & Raffles.
You are probably going to cheap out but the very best way to do it is this....Buy a half dozen boxes of premium ammo from each of the different manufacturers, Remington, Federal, Winchester, Hornady etc. Try to stick with something that you can find on most gun store shelves. Buy the premium stuff, not the discount stuff. Stick with something around 150gr. Then, go to the range and find out which ammo shoots the tightest groups at 100yds with your rifle. When you find out (the choice will be obvious), buy a couple cases of the same lot. If you are young, buy 3 or 4 cases, you'll be set.
My kid has a Weatherby (Howa) 308, we could not get acceptable groups with anything we tried...I went to a cheap box of Remington 180 Core Lokt's...instant tack driver...just food for thought.