Depends who you want to get over I suppose. The answer usually is your own pocket if its a well known face and hope to get it back through door sales.
Sometimes venues will stump up the cash for you ive found.
I have run various DJ events over the last 20+ years mostly small and always found set swaps are a good idea so no money changes hands and both parties get to spin at a new or different place. This is my favourite method aside from paying in records.
Also used to do simple splits say if the DJ was from same town as us (London) ie we all split the door fees after costs. Sometimes people dont get paid but then we all dont get paid, which is easier to take for all concerned.
We have mainly hired other collector / DJs whos tunes we like or styles we repsect and know from buying and selling records. This is simpler in my view.