You need to make the distinction between PA(provider allocated) and PI(provider independent) objects, as well as the distinction between LIRs(members of the RIPE NCC) and end-users.
PA can only be held for further assignment in their networks by a LIR that is a member of the RIPE NCC, received in two ways: maximum of one IPv4 allocation /22 with proper justification, or acquisition through merger with another LIR. The membership fees are as you mentioned.
PI resources are assigned to end-users in the region, that do not need to be members of the NCC. They do however need a valid end-user agreement with a LIR, and each(unless they are allocated on the same date) object entails a 50€/yr fee, billed to the LIR. PI IPv4 is no longer being assigned from RIPE, but existing ones are openly traded.
My guess would be that the nets you were looking at were PI networks, so no, you do not need to pay the membership fee.
The document ripe-680 covers basically everything you need to know:
https://www.ripe.net/publications/docs/ripe-680