Nigel Farage's Ukip spent more per vote than any other mainstream party in Aberdeen Donside, Dunfermline and Cowdenbeath while losing its deposit each time because it polled under 5%.
Last June, Ukip spent £16.77 per vote in Donside after the death of SNP MSP Brian Adam.
Ukip then spent £10.42 per vote in the October by-election in Dunfermline caused by jailed wife-beating MSP Bill Walker resigning.
Now candidate spending returns from January's Cowdenbeath by-election show Ukip was again the biggest spender, laying out £6.41 per vote in a doomed bid to fill the vacancy left by the death of Labour MSP Helen Eadie.
Despite shambolic in-fighting among its Scottish leadership and a series of controversial remarks by Scottish party chair Misty Thackeray, Ukip is hoping to win one of the six Scottish MEP places in the May 22 European elections. But the latest figures from Cowdenbeath suggest lead Scottish candidate David Coburn will have to contend with an inefficient Ukip machine in Scotland as well as voter hostility to the anti-immigration and anti-EU party.
The Cowdenbeath by-election was won comfortably for Labour by Fife Council leader Alex Rowley.
Campaign returns show Labour spent £38,229 out of a possible maximum of £100,000, of which £14,801 went on leaflets and flyers, £9546 was for staff costs, and £6274 was for accommodation, the latter suggesting Labour had to draft in help from outside the seat.
The SNP spent £33,796 on runner-up Natalie McGarry, of which £23,590 was leaflets and flyers and just £2871 accommodation.
Although the two big parties spent almost the same in total, Labour's spending was more efficient at £3.42 per vote compared to £5.93 for each SNP vote.
The Tories spent £4.82 for each vote received by candidate Dave Dempsey, and the LibDems £4.96 on each vote for candidate Jade Holden.
Ukip's spending worked out at £6.41 for each of the 610 votes received by its Denise Baykal.
Fringe party the Social Democratic Alliance spent £9.40 per vote for James Trolland, while independent Stuart Graham spent £4.68.
Meanwhile, a new pro-EU party formed as part of a backlash to Ukip has announced it will field Scotland's youngest candidates on May 22.
All four candidates for United with Europe will be students aged 18 to 21.