Well I think that you should think aobut the actual time it takes you and how much to charge, even if there is a short deadline, its still going to take you time and this is what you should factor.

Hey if you can get $1000 US for a still go for it!

Just that $1000 for a still and $100 per vfx shot (independant of time) dosent add up to me, a good VFX shot would take a lot more rendering than a still as well as the process of animation so the overall work would be more, dont really know how your are going on that.

Again time and how long it takes is the factor.