I wrote about cost on my blog:
http://guerby.org/blog/index.php/2007/04/22/157-elections-et-comptabilite
Only paper trail makes voting machine acceptable.
Example of correct use Venezuela where the machines are here for just after close result but voters put the printed bulletin in the ballot box and a random half of the box are recounted manually.
http://www.ordinateurs-de-vote.org/