Two very recent ones, where Willow and Tara, at least, are confronted about not contributing their share of the household bills, rent and food is:
Family by: Stuffandnonsense
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=37375 And
Road Full of Promise by LadySanume, in this one Tara did pay her share of the rent, but she did it quietly, by placing it on Buffy's nightstand without being asked for it.
http://www.dark-solace.org/elysian/viewstory.php?sid=3824Where as Willow is freaked out and hurt about Buffy asking for rent, even if it's to help Buffy make ends meet and keep her financially afloat, in both stories.