PPU will be the cheapest brass and I have some for when I don't want to chase the brass or have a brass catcher attached. PPU uses Large rifle primers and you will most likely experience loose primer pockets by 5 rounds loaded in it or less. Hornady expect 10 or more loadings from each piece. Lapua brass 15 to as much as 20 loading is not uncommon so that makes Lapua cheaper per shot fired than the PPU but I hate to loose it. Have some Nosler here but haven't tried it yet.
Bullets there are lots that will work well from the Grendel for those critters, remember it is not that fast so cup and core bullets work fine for hunting. I have mostly hunted with Hornady A-Max and SST. Both work well.
Lilja will have a SAAMI chamber instead of some of the other ones that are around so you have it as Alexander designed it to be on his final iteration. This year I am planning on using the 129gr Long Range Accubond have some loads that are very accurate with CFE223 COAL 2.271 inches. Same load also shoots well with the 130gr Berger Hybrids.
Nosler has data listed online now for the Grendel. There are a couple reloading manuals dedicated to it available at www.ar15buildbox.com.
Volume 2 covers hunting bullet selection and expansion for game.