As you can see, I currently owe Amazon 1.04 US-$, which can be extrapolated to around 2.60 US-$ per month. I have backed up 3.3GB of data so far, plus several hundred MB of archived data I deleted from my HDD afterwards. My daily change volume is below 3MB (well, I was surprised for myself!).
I am looking forward to seeing how this is going to develop once I use it for major archiving purposes. Still, what I can say right now, is, that the costs are extremely reasonable. Up to now, I am still very determined to purchasing jungle disk once my 30-day evaluation period is over.