Trax, they're busting your balls because you are in no way ready to charge anything for recording. You should thank anybody who lets you use them for a guinea pig just for the practice. Listen, I've got about $5000 bucks worth of mics, a $2000 digital recorder, $4000 worth of preamps, $6000 worth of guitars, and $5000 or so in assorted cables, power conditioners, stands, shock mounts, FX, compressors, guitar amp modelers, headphone amps, headphones, room conditioning, monitors, etc., etc., and I wouldn't dream of setting myself up as a commercial studio. Why? because I'm an honest man. What you've asked, in effect is," I have a first aid kit and no clue, what should I charge for brain surgery?" Hell, I've got the whole operating room here, and that doesn't make me a brain surgeon!
I give studio time away for free just for the practice, and if I stick with it, someday I might be able to call myself a recording engineer without lying. After $20,000 or so of gear, and 18 months tracking and mixing, I'm comfortable calling myself a tracking engineering assistant. Commercial recording is a profession, like being a lawyer or a doctor. It requires time, work, and patience. Don't give up, just look at the path instead of the destination. Instead of asking how much you should charge to do something you don't have the gear, the experience, or the knowledge base to do yet, you should be asking how you can learn to be a recording engineer and build a studio that gives you the tools you need to become a professional. Stick around, it's worth the wait.-Richie