Political parties are required by law to file returns detailing what they spend during by-election campaigns, which can be viewed by the public.
Labour spent £26.51 per vote if their total was broken down by the 3,713 votes for the party’s candidate Richard Tunnicliffe.
The party’s return lists advertising spend worth £40,470 and unsolicited material like leaflets to electors worth £45,840.
The party paid for £31,295 of advertising on Meta and Google.
Labour provided receipts for six Airbnb bookings for 22 people stretching from September into October last year, worth a total of £25,315.
The properties were located in Trefforest, Blaenau Gwent, Cardiff, Hirwaun, and two in Newport.
The value of the bookings differed from the figure written in the return, however, which declared a much smaller sum of £3,321 for “staff accommodation” from Airbnb.
When BBC Wales asked Labour to explain the difference, it was told it was common practice for candidates and parties to divide and share spending where some elements of an invoice count as regulated expenditure and others do not.
Welsh Labour was asked if they were staff from the UK party but it did not answer the question.