i think the if you sell to your audience that the light its off, you can lightit as if there where lights on (in some parts) always with out showing the source of the lights, lighting from above, with the lightis hanging. Movies are veracity, noth truth. and usualy the audience bought wath you sell them.
like the DP of "Metegol" (last movie of Campanella) said when i asked em how was to do DPs work on digital: It was the same, just easy`r, i was on a room with a lot of kids on there computers and i said "more light here, less here, softher here, etc", my job its to create a painting, no to move a light bulb.
you shoud buy a Canon T3i/600d, its cheap and you can adapt a great range of old lenses to it, so you can use a nikon 50 1.4 or an m42 24 2.8 . that gives you the light that you are missing in an affordable price.
But even so, you always shout try to have a few lights, our job its more biutiful if we can paint with light oder than fixing the lack of it with ISO or aperture.
sorry for my english, i need to practice!