My goal is to convert my whole school and then the district. I know it will take data to prove the savings before the district will spring for more computers.
First off, practical stuff: Connectivity and hardware are going to be your initial expenses. If possible, you should also have a tech person on-hand for repairs and service issues.
Second: All districts are different. Do most of your students have computers already? Or do few? Are your teachers each equipped with a laptop? Or do you have to scramble on your own to flush out tech needs?
Third: Consider this... I don't know exactly what your situation is, but I would suggest going totally paperless in your own classroom first. Then use the leverage it gives you with regard to ease of parent conferences, simplicity of iCal, ongoing assessment via individualized student digital portfolio blogs, etc... to get other teachers onboard. Rather than trying to sell the paperless classroom as a way of 'saving money' on paper, try presenting it to your faculty as a way of making classroom time more effective, grading more time-managable, and student outcomes more authentic and dynamic. Because in the end, this isn't just about saving paper... it's about saving students.
Once the other teachers realize just how effective and easy it is to use a digital classroom, you'll begin to develop a critical mass. That'll wind up being a lot more effective in the long run than just one person trying to do all the work.
This is essentially a collaborative venture we're all embarking upon. No one of us can do this alone. We need that critical mass both to evaluate best practices between each other and to influence the powers-that-be that either they jump on the train with us or take the long walk home alone.