Finding a proper accommodation in Montenegro is not such a difficult process, but requires a period of at least one month before your arrival.
The easiest way is to contact one of the real estate agencies and check their offer. In accordance with your needs, you can choose between a house and apartment, empty and furnished apartment, and similar. Prices vary depending on the quality and location of accommodation.
Besides agencies, you could also check daily newspapers and advertisements, concerning that many choose to rent their real estate without intermediaries. In this case, it would be useful if you had a person from Montenegro to assist you in translation and making arrangements.