I've known crank rebuilds to only replace the main bearings, but yes, a complete rebuild would also replace the big end bearings.
But there is then the overall cost to consider.
Set of main bearings at AUS $170, 2 big end bearings around AUS $200, crank seals around AUS $60 plus rebuild labour charge, maybe AUS $200.
That is over AUS $600, TYGA sell a full bottom end kit (brand new crank & all seals etc) for AUS $900.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30