A lot depends on how much shooting you are going to be doing and how much reloading equipment you already own. Then how precision do you want your loads? I only ask this as after I went to the Williamsport 1,000 Bench Rest School I came home and bought about $3,500 of reloading equipment to replace all the old time stuff that I already had. For some reloading is a great hobby and past time and for others it is needed to get the accuracy you want and then for others it tiresome.
So there are 7,000 grains of powder in a pound of pounder. 338 Lapua loads for 300 grain projectiles seam to have loads ranging from 75 grains to about 100, thought they are not always what you will end up loading. So if you figure on the high side, 100 grains, you will get around 70 rounds out of a pound of powder. You might get less from spillage or more from lower charge weights. Then pick a powder and see what container size you can buy and at what price ALL IN with shipping and HazMet or local sales tax. Do the math. If you get 70 rounds from a pound of powder that costs $35.00 all in, then the powder will cost you $.50. Buy an 8 pounder of powder and it will be less. Etc. You should be able to get some more reloading data on the home page of this site.
Go to MidwayUSA, Grafs or other supplies that sell brass and take the cost of the brass and divide it by 10 reloadings to be on the safe side. Maybe with the 550 pieces you have you will not need brass for a long time.
On the same site you can get prices for Primers and Projectiles. It is funny that Berger's Loading Manual, doesn't show any loads for the .338 Lapua, but I would bet it will be in the second addition. Usually a case of 5,000 primers will be less cost than a box or 1,000 or a sleeve of 100, but if you are going to try different ones, you need some of each. Same thing on the price of projectiles.
In looking at Midway (you can shop for better prices). 1,000 Magnum Large Rifle Primers are $37.00. 100 Lapua .338 300 grain projectiles are $84.00, H4831 is $29.00 a pound and Lapua Brass is $289.99 for 100. Then add $28.00 HazMet and Shipping. for H4831 more like 80 grains according to the manual I have.
So now depending on how you want to go about this, just do the math. If buy 8 pounds of powder and allocate 50% of the HazMet fee to it and shipping, then you are looking at about $33 per pound. 80 grains 87 rounds or $.38 per round.
Primers with the other 50% of the HazMet Fee and Shipping would run around $.06 or less. And projectiles with shipping at around $.90.
NO BRASS
Powder $.38
Projectile $.90
Primer $.06
TOTAL $1.34
Brass $.15 per use (at 20 reloads) to $.30 per use for 10 reloads.
Now add your labor or NOT and the cost of all the reloading equipment. Shoot a lot, still much less than factory rounds and SHOULD be better if you are going to have the right equipment and know how to load.
Enjoy, Bob