For Medellin there are huge ranges of prices in different parts of the city, different sizes, furnishings, amenities, etc. For a very nice apartment in a good location of Poblado, I'd expect to spend around 2 to 2.5 million per month. If it's less than a month it's going to limit your choices and increase your costs due to Medellin's short-term rental law restricting renting in most buildings for less than a month.
PM me if you want a local contact for a rental.
PM me if you want a local contact for a rental.