|>>|| No. 82521
According to research by the Electoral Reform Society, spending on a constituency level varied from 14p to £3.07 per vote at the 2010 election. Unsurprisingly, the least money was spent on safe seats. That's based on a simple calculation of votes won vs total spend; calculating the marginal cost per vote isn't really practical.
At the 2015 election, Labour spent an average of £1.29 per vote, the Tories £1.38, the SNP £1.01, UKIP 98p and the Lib Dems £1.46.