Based on the public rates noting JQ (and all the other majors like QF/VA etc) would have negotiated rates, it's ~8.25% cheaper to use a stand without an aerobridge for domestic flights.
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On top of the $30.80 above there is an extra $3.89 intl security fee meaning at most the public rate BAC charge is $34.69 but if JQ is indeed getting a ~8.25% discount similar to what's offered at domestic then it's likely to be about ~$32.34.
It's also worth pointing out that JQ is geting QLD's AAIF funding (unknown dollar figure) for their flights with a 50/50 split from QLD Gov and BAC.