Beyond these minor changes to the optical components, the most significant difference from our previous polarimeter is the replacement of discrete commercially-sourced mounts by a customised mounting system that both reduces costs and simplifies alignment. In our previous design, optical holders accounted for the majority of the build-cost, with each of the dozen or so mounts costing at least $50. In the new design all mounts are customised parts that can be straightforwardly fabricated using desktop milling and 3D-printing at a combined cost of just $20. Moreover, our new design is easier to align and self-standing, avoiding the need for an optical bread-board or other kind of heavy base-plate. It is worth pointing out that the mounting scheme we use is a general purpose solution that may be applied (with minor adaptations) to a wide range of optical systems beyond polarimetry.