Repair of texts in English

My partner is a successful German businessman originally from Ukraine. He has lived in Germany his whole life and has built 3 successful businesses there (catering, construction company, and legal consulting). He has written a book about entrepreneurship — about how to open a company in Germany, how the business registration process works in Germany in general, what is important to know when starting a firm, etc. Currently, we have a draft of approximately 185 thousand characters. The text needs to be improved, refined, made more professional, and brought to a state suitable for publication. The book is written in Russian. Please send your own works in Russian on business topics. It is also important for me to hear the approximate budget and timeline for such work.