That's the easy part of the question. What type of speakers? - It depends on the size of the room, the type of music, the type of room, lots of variables. I hope you're not gonna try to dj a party. These are things you should have been prepared for before taking a gig.
much depends on if this is a party for some friends or a professional gig.
if you have a small room and just invite the boys over for beer even some powered bookshelves under $100 might work great. if you have a larger room then one or two larger powered loudspeakers in the $300 range might be more your cup of tea. for any professional gigs though a bit more planning needs to be in place and typically costs are quite a bit higher.
i gave some generic advice since you did not give specifics. if you're really looking for better advice you may want some more details added and someone might be able to help you out a little more.
-type of music?