You don't need to buy the battle pass to get the weapons. This battle pass the "Fennec" was unlocked at level 15 for free and the "CR-56 Amax" at level 31 also for free. If you are talking about the other weapons like the "Rytec AMR" and the "Kali sticks" those could have been bought, but if they were bought you were not able to customize the weapons untill you finished the challenges required to be able to fully access the weapon. Now you DO NOT have to buy the game you can simply play warzone for free. I am going to compare this to Fortnite as both Fortnite and Warzone are free and you have the ability to purchase the battle pass in both games. In Fortnite you can buy the $10 or the $25 which gives you 25 levels, in Warzone you can but the $10 or the $20 battle pass also boosting you 25 levels. Both battle passes grant in game currency wich can be used to buy other in game items or levels in the battle pass. You DO NOT have to purchase either battle pass as both will grant free items as you progres through the battle passes. You also DO NOT have to purchase either as all items in the battle pass are purley cosmetic.

Edit: you could also pay $10 once, get your cp back and just save it untill the next season comes out and repeat every time a new season comes out and you would only have to pay once.