For small quantities like the ones we are discussing here, the raw cost for the materials plus a (dongle) PCB would be in the order of 30-40 EUR. P+P by registered postal mail is about 5 EUR. Assembly and PIC programming costs may vary a lot depending on the quantity of boards ordered , so I cannot give a clear figure now. For manual assembly, programming and testing, a rough estimate would be around 10-20 EUR per unit.
If Rough Estimate of Cost is given,it will much easier to select some options.