I say skip the DJ and just hook up speakers (or your whole stereo system, which is what I do) to your computer, or to your ipod. Either way, speaker adaptors will likely cost less than a DJ.

A grill is probably necessary too, and def just tell people to bring stuff to eat and cook. If your spending time and money hosting it, people are usually more than willing to spend a few bucks on grub to share.

I guess I do more get togethers than "partys", but I hope it helps.