Well the 338wm is one of my favorites. Not sure where the one poster is buying ammo, but he is paying way to much for 338 wm. Agree that the lapua would be north of $5/factory cartridge, but the typical price of factory 338wm is $50-60/box of 20 so $3/cartridge. While decent factory ammo is available for the win mag, i would think that anyone using them one, and everyone that uses a lapua will reload.
Completely different purposes. The lapua was a purpose built military sniper round that has been adapted for long range target and hunting. The win mag is probably the most common light medium hunting round, very few would use it for target. The common target rounds appear to be 223, 22 and 6mm bench rest and wildcats, 6.5x284, 308 win, 300 win mag, 338 lapua mag, and 50 bmg.
Common misconception of 338 win mag is that it is some sort of over bore cannon that is unnecessary for NA hunting. Not at all true. However, recoil pulse is both significant and fast, beyond many peoples tolerance. Many use recoil reduction in sporter weight 338 wm rifles. Recoil and blast from a 338 lapua is excessive, one would expect that from a cartridge burning close to twice the powder of the 30-06 and 30 % more than the 338 wm. Most 338 lapua target rifles will have recoil reduction and be too heavy for the field. Field weight rifles will definitely have reduction, significant recoil, and excessive muzzle blast.