Why not just check the prices of goods more carefully before purchasing the next time? It was your own fault that you paid "too much". Besides - what to you expect the manufacturer to do? Try to enforce
RRPs which would simply be yet another barrier to competition? Why didn't you bring the item back before leaving the shop, complain and get a refund or replacement (i.e. the cheaper product)?
Why not exercise your right as a consumer to make informed purchases at what you consider the most competitive outlets? That's the best way to engage in direct action and effect change. On the other hand...
... if that's how you feel then why don't
YOU organise one rather than waiting for somebody else to do all the hard work? Or maybe you just want to bleat about the issue rather than actually doing something?