Germany has all types of mice, from petstore to show winners. They don't have all varieties though. Folks in Germany don't keep dominant red or angora (for example) because they're perceived to be "cruel" varieties. Long story (and debate) there!
It would cost minimum USD $1000, probably closer to around $1500. That's about how much I paid for my recent imports when all was said and done, but I know some folks who paid over $5,000 for imports from England a couple years ago. This is because mice (no matter how many there are) must come as live cargo and you must clear multiple governmental hurdles: US Customs and Border Patrol, US Fish and Wildlife, the US Department of Agriculture, a private broker (sometimes), health certification by the exporting veterinarian, health certification by the importing veterinarian, airline fees, lawyer's fees, and so forth. Each governmental office has its own paperwork, forms, and procedures and each doesn't necessarily communicate with the other, especially in different countries. The mice themselves were free or low cost, but whenever you import warm-blooded animals into the US it is a months- or years-long process that requires a lot of planning and a lot of legal work.
I would recommend the process to anyone who has the time and money to do so, but it is difficult and not for the faint at heart. You must have somebody on each side of the Atlantic who knows the local laws and procedures well, or else US Customs could end up holding you or your animals indefinitely. You sometimes have to be forceful with people when importing animals. In my experience, many folks didn't have a clue as to what they were doing (though a couple were very kind and reasonable, they still had no idea what they were doing).