The results show that Tom Allen spent $21 for every vote he received in November, making his run the most costly unsuccessful major-party challenge to an incumbent anywhere in the country, per vote. Allen's votes were cheaper only compared to the candidates in tight races in Alaska and New Hampshire and incumbent Max Baucus' campaign in Montana.
Susan Collins spent more money, but also won a lot more votes, resulting in an expenditure of $17 per vote.
Those numbers pale in comparison to the third party per-vote expenditures. If we accept the totals reported by the Secretary of State and broken down on Herbert Hoffman's website, (which are probably way off) Hoffman spent $76 for every one of his votes while Laurie Dobson (who still probably thinks she's running for something) spent a whopping $528 for each of her 27 votes.