If you can't afford the shopify fees you don't actually have a business.
I also sell 3d printed models online so I've made like 20+ e-commerce websites so far. Most of them are niche website and get 5-10 sales each and some even get zero sales but some websites are seasonal in nature and in some season or event, they blow up in sales. I am trying to capture this windfall but Shopify is not good for this task. They charge per store so I am limited to just having one store which is not good…
I would probably develop a framework and do free gatsbyjs/netlify static sites that link back to a centralized payment processor service