they told me that my company has to bring at least $300.000 to do that
That sounds unlikely.
I've opened bank accounts with BZ WBK with way way less than that, but it's true that they were for EU registered companies. Give a local branch a call to discuss what's needed - the Krakow branches of major banks (e.g. Deutsche, BZ WBK, Raiffeisen) are used to dealing with foreigners and they should be able to tell you over the phone what the requirements are.