The deal was that we paid for their most expensive monthly line item: the T1 circuit. We covered 100% of the T1 yet were allocated only 50% of the bandwidth, if I recall. We recruited enough co-op members to cover that fee before beginning and had a wait-list on Day One.
Our PortMaster was configured to monitor monthly bandwidth consumption per co-op member. We accommodated spikes in traffic of individual members, but if the aggregate went above some threshold, the co-op would pay more to Speakeasy. The intent here was that our overage fees would help pay for a second T1.
We also had some co-location hosts in their rack, which was around the corner from the coffee machine in those days.
Member fee schedule was proportional to type/speed of connection used and anticipated usage. Beyond that, membership was at cost.
Internally, co-op members would resolve financial details among ourselves, and we sent one payment check per month.
The agreement was fairly balanced. It allowed our members physical access to reboot a piece of co-located equipment, but any maintenance required pulling and removing the machine. (Again, rack was in tight quarters of a coffee shop.)
Since this was mid-1990's, all members supplied their own pair of modems for each side which were mostly 28.8 back then. I think one person was going with ISDN, and maybe another had Telebit Trailblazer 56k.
I'd like to think that upon seeing how this was a benefit to the cafe's financial statements that it gave Mike, Gretchen, Chris, et al the idea to move into the larger ISP space for which they then became known.