Whilst I wouldn't pay it as I'd do it myself, I would have thought a full polish on a say twin might be a lot more than that ($100). You'd be doing yourself a dis-service by charging only $100. To properly polish your average twin externally only I would think you'd be up for atleast 2-3 hours work.
I also would think that you would need to ensure that your polishes and product are CASA / Aircraft manufacturer approved.
For a 172 I would pay $80 for an internal clean including seats and roof lining etc and perhaps $150 for a good external polish.