I think, to make it feasible producing and selling them by yourself, you should calculate the production costs and average shipping costs for e.g. France, USA, Argentina and China. If you’d add them you’ll know how much the product will cost for buyers.
If France would total to €6.- as the cheapest and Argentina to € 15,- you could chose to let everyone pay €15,- so you’ll make some profit on sales within every continent except South-America.
You could also use those totals to decide which profit margin on the product itself would lead to acceptible prices in every region including shipping. This last option gives you the freedom to get rid of the payments for shipping and let the buyers be responsible for that.
It will however be likely to result in lower profits.
The final price I’d like to pay for it depends on the quality and could go up to €60,- if it would be really premium. Considering a prototype-like product, I think €20,- is borderline and €15,- would be optimal.
If you don’t want to go through all this effort you could release the .stl file.