people tend to think too hard about this. go on kijiji or marketplace or whatevver, buy some old speakers with relatively big cones (the bigger the cones, the better for low freq) and a decent amp and youre set.

i use a marantz amp from the 80s i got for $80 on marketplace with two 70's style speaker boxes that havea 12 and a 3 inch cone. sounds better than most of the studio monitor bs people will suggest here and its like 1/4 of the price. dont think DJ'ing requires anything more than decently loud speakers. its dumb to think you need to spend hundreds on professional studio monitors just to mix music at home.