Assuming this setup is for practice and small hall or club venue gigs, you should consider mic'ing the drum kit, at least for the gig venues.
Since your PA looks like it's got only 4 inputs, and mic'ing a drum kit effectively calls for anywhere from 2-6 mics, the best way to handle that on a budget would be to acquire a (minimum) 6 channel stereo submixer to go into 1 of the PA's channels, and another 4-channel for your vocal submix to go into another, leaving the PA's other 2 inputs for the guitar and bass. Behringer has a number of inexpensive ($60-$100USD new) yet quite decent options, but if you're down on Behringer because of image concerns, then a Yamaha MG10 or Peavey 6 or 8 would do well. New, these little boards go for around $130USD - $150USD, used for about half of that. With some clever signal routing, with vocal mics panned hard to one side and drum mics panned hard to the other, you might even be able to get away with one submixer for vocals and drums, but you'd be compromising. Two would certainly be best and give you flexibility, and a rig you could use to cover recording your practices and gigs, if not demos.
You could work your way up with the mics, starting with 2 -- 1 unidirectional/tight cardioid pattern for the kick (bass drum) and 1 omnidirectional overhead (over the center cymbals and aimed toward the snare. You could then add 1 unidirectional at the hi-hat/snare, 1 close over the toms, and 1 at the floor tom. CAD makes a nice inexpensive 4-mic drum mic kit.