Bruce Schneier offers a back-of-the-envelope estimate of what we’re up against.
In 2002, all the Congressional candidates together raised over $500M. As a result, one can conservatively conclude that affecting the balance of power in the House of Representatives is worth at least $100M to the party who would otherwise be losing. So when designing the security behind the software, one must assume an attacker with a $100M budget.
Conclusion: The risks to electronic voting machine software are even greater than first appears.