Have you looked at Doughty Clamps? I happen to have one knocking around here. They're not cheap, but they're a fraction of those that you have linked to - I assumed at that price it'd be for a box of 10 or something.
Well I thought Iād picked through their site but I just had a second look and found some trigger clamp things a bit like snap clamps, which open up to 80mm. They might do the job š
Does anyone do half couplers or snap clamps in 80-85mm diameter? I can only seem to find one American company that does large half couplers and they're wildly expensive: https://www.stagelightingstore.com/Stage-lighting-store/clamps-claws-couplers/couplers/half-couplers/extra-large-half-couplers