Building costs in the UK are just so much cheaper than here.
Indeed they are. I guess our last stadium you could class as tier 3 was NQ which is 25k built for $250mill in 18/19. If there is cost saving from that one in some way (not sure if there were extra costs associated with that project like transport, external parks, cyclone proofing etc?) then it may be possible to build a decent 25k stadium for $200mill ish?
Recent stadium build completions in Australia
2022 Allianz 45.5k $830mill
2020 Qlnd country bank 25k $250mill
2019 Commbank 30k $300mil
2018 Optus Stadium 60k $1.8bill
2013 HBF Park rebuild 21k $125 mill
2010 AAMI park 30k $268mill
2008-10 McDonalds Jones rebuild 33k $110mill
2008 Cbus stadium 27k $170mill