This Gunbuddy is completly FREE and unlocked at reaching level 45 of the Ignition: Act 1 battle pass. To unlock the premium rewards of the battle pass, it has to be purchased for 1000 valorant points.
Gunbuddies are charms that you can attach to any of your guns in Valorant. They usually come in pair of 2 so you can have them active in two different weapons at the same time. It’s also possible detach them and move to different guns.