Actually it's been implemented as far as I know:

[1]Switzerland's “Crypto Valley” Successfully Completes Blockchain Voting Trial

[2]Japanese City Trials Blockchain Voting for Social Development Programs

[3]Sierra Leone Uses Blockchain To Track Election Results

[4]US: West Virginia Completes First Blockchain-Supported State Elections

For sure those progressive countries are already looking at this options. Not to save money but to make it more transparent to its electorate. On the other hand, there are those who opposes it, saying that we're getting totally dependent on the Internet. It's still a long way to go, but I guess its inevitable and we might see governments around the world slowly injecting it on their electoral process.