The problem with buying European is that shipping between countries is nightmarishly expensive. If Brussels wants to try something useful - instead of bottle caps create a proper shipping network that can ship from Malaga to Vilinus in 2 days for 0.5 euro per KG. It is not that we don't have national postal companies. It is absurd to buy something for 15 euro in italy and pay 30 euro shipping to romania.
Shipping individual packages within a short amount of time costs money. The solution is to do what companies like Amazon and AliExpress do: stock up products in many different companies in bulk so that packages can be dispatched locally for much cheaper.
Many of the shipping routes between countries go by plane rather than by boat, filling up unused weight in passenger planes or being shipped in bulk by passenger planes. Planes are a lot more expensive, especially by weight, but you'll get your products within days rather than weeks.
If you're a business importing goods in bulk, you'll have to deal with weeks or even months of delays between ordering and delivery, but international cargo delivery per product is essentially free unless you ship things like cars.
Things will become cheaper as warehouses are spread wider and transport legs get optimized more. Currently, there aren't many companies shipping from Italy to Romania, so there aren't many boats or trains making the journey, and shipping is expensive. When demand grows, more availability will follow, and prices will drop eventually.