artists_beware | Advice - small commission, big changes..!

Hey,
This is by no means a warning or anything, I just really want some advice. So I hope you don't mind that I'm not following the preferred layout that was recently produced for posts. :)

I have a small albatross around my neck at the moment in the form of a low priced commission that I thought I'd get finished in a short amount of time but which is starting to drag.

I assumed that the commissioner wanted a sketchy, quick style and that therefore I wouldn't charge very much for it (I've been known to charge between £100 and £200 for more complicated stuff but this piece is only about £12).

I regularly update people on my work for them so I've shown the client a few WIP shots and each time, I received a positive response with some requests for minor changes, which I did - the client liked my progress each time. I thought that the design was almost finished in the last update I sent, however, was not replied to for a long time and when I finally did get a response the client is now saying that they don't like the image anymore and have showed me a new reference image, with an apology that this one wasn't what was shown in the first place. It will basically mean re-drawing the whole thing and starting over, and I've already spent way over £12 worth of time on this anyway. =/

I don't generally mind picky customers and since the client is very apologetic I think they're aware that I'll be a little annoyed about this request, but I really don't know what to do - I will probably end up just knuckling down and doing it, but I don't want to be stuck in a never ending process for such a small amount of money. I am not even taking on any other commissions at the moment and am too busy preparing for an interview and starting some garment manufacture, so this is a bit of an irritating niggle to have in the background now and I just want it over with!
Your advice appreciated. :)