This is just one of those things where you assume that there is an ommision somewhere unless they show it in an episode.
Where does Buffy find the time to do her guidance councilor work while all this stuff is going on. Well, the writers were kind enough to put a few spots in where we can see her doing the job in spite of the recent turmoil, and so we do indeed know that she is still doing her job. If there was no plot reason to air these sequences of her sitting in her office, then we would be seeing threads on the forums saying 'Has buffy lost her job'?
The fact is that even if you can't see it it, it may exist later as a plot device, or it may not. Everything that happens beyond the scope of the show is 'grey area' and grey area is available for molding by the writers to be what they see fit. Xander may be slipping them 100-spots under the table, or they may be getting child support, or Tara may have left willow as the beneficiary of her life insurance. Giles may have set up a trust fund. Willow might run a massively succesful website that brings in scads of money via advertisments (although that idea is pushing the limits of belief). Spike may be pimping Dawn out on the streets at night and slipping the proceeds into the cookie-jar. Who knows?
We will know when it becomes relevant. One thing we DO know however, is that somehow they are finding the money. This is canon at this point. After all, put the writers to the test and they'll make up a plausible reason for you, but why waste the effort?