Hey,
Here at DDJT we specialize in digital DJ-ing. Which, for most of our readers (except the ones that still like turntables and use DVS), means that you use a computer/laptop with a DJ controller. You can get a DJ controller for about 100 dollar, but it will be very basic. It will have two “players” and a “2-channel mixer” bit integrated. All you need extra is a set of speakers and a laptop/pc. Obviously the speakers cost money as does the software (unless you make do with the LE version of whatever the software comes with).
I doubt if you can make an entire setup for 100 USD though. Might have to look at used stuff.
You can use various software on the computer/laptop to “remix” songs that you can then play in your DJ software with your controller.
Hope that helps.
Greetinx.