By mail: This seemed like a possible option. However I found that Slovak Post forbids sending banknotes or coins of any value via regular mail (for which shipping would cost โฌ1.60) and instead only allows them in insured packages in which case the shipping would be โฌ20.50 ๐
I'm not aware of Slovakian law. But every other postal service in western Europe bans sending cash by mail for insurance reason. They don't want you to ask for the money back if it doesn't reach the destination. But they actually don't track down people sending money. I've sent cash by mail many times without any issue. Hide it in a folded A4 paper, so that it's not visible when looking through the envelope, and it should be fine, it has a 99.99% of arriving like any other letter.
That's my 2 cents.