Juicebar is the premiere marketplace for Resolume. While many plugins are paid, it features a "Free" section that is updated regularly.
The Resolume community is incredibly generous. Experienced developers often share beta versions or "passion project" plugins for free in the section of the official forums. resolume+arena+plugins+free
Free "Data-mosh" or "Pixel Sort" plugins are staples for techno and bass music VJs. Juicebar is the premiere marketplace for Resolume