There is more than one cost, and the fee is only part of it. Alongside the application fee you should expect expenses for translating documents and for biometric registration, and in some cases a financial security deposit.
Under EU rules there is generally no application fee at all. Under the Danish national rules the government fee is currently around DKK 9,000.
For the legal work, our fee for a family reunification case is typically between DKK 15,000 and 20,000, depending on how involved the case turns out to be. You will have the figure before anything starts.