What's a good IP strategy when the budget for patent is limited?

I'm not that familiar with all the "dos" and "don'ts" or "cans" or "cannots" of German law, but if you are able to file a provisional patent application in Germany, or are permitted to file a provisional application in the US even though your IP was developed in Germany, then I would proceed with a provisional patent application. Speaking for US patent procedures, you can file a provisional patent application for a relatively inexpensive amount of money provided that you can put together an enabling disclosure of the invention, and the filing fee is only $130 for a small entity.
This provisional patent application establishes a priority date which effectively establishes the fact that you were the first inventor for such technology despite others who may file patent applications subsequent to your provisional patent application. The one significant drawback of a provisional patent application is the fact that, in and of itself, it will never be examined and will never lead to the issuance of a patent unless you effectively perfect/convert the provisional application into a non-provisional or PCT application within one year of the filing of the provisional application - note that the one year deadline is a hard deadline, meaning there are no extensions of time permissible - if you fail to file your non-provisional or PCT application within the one year time frame, your provisional application, and your priority date is lost. So, during that one year, you can use such time to assess your financial situation, try to obtain funding, see what potential commercialization appears to be like, and so on.