Did lots of work/research to figure out those specific items on sale( you will be very hard to find out from BIG W LEGO Shop section or Website, as they are always shy about clearance sale), will update if others find out more.
Most items are not available online, you have to visit your local Big W store, they do not put price tag on the shelf, please double check the price by scanning the barcode instore to make sure the right price.
Lots of sets with decent discount, lucky if you can find something.
LEGO Technic Volvo EW160E 42053 $40 off @ $99
LEGO Technic CLAAS ZERION 5000 Trac VC 42054 $100 off @ $125
LEGO Technic Bucket Wheel Excavator 42055 $110 off @ $265
LEGO Super Heroes The SHIELD Helicarrier - 76042 $100 off @ $375
LEGO Speed Champions Mercedes AMG Petronas Formula One Team - 75883 $45 off @ $104
LEGO City Airport Air Show 60103 $46 off @ $49
LEGO City Fire Station - 60110 $36 off @ $89
LEGO City Volcano Exploration Base 60124 $40 off @ $79
LEGO City Airport Passenger Terminal 60104 $40 off @ $79
LEGO City Police Bulldozer Break-in 60140 $46 off @ $49
LEGO Star Wars Resistance X-Wing Fighter 75149 $40 off @ $79
LEGO Star Wars Tie Striker - 75154 $23 off @ $65
LEGO Star Wars Rebel U-Wing Fighter 75155 $34 off @ $75
LEGO Creator Lighthouse Point 31051 $20 off @ $49
LEGO Creator Vacation Getaway 3-in-1 Camper Van $39 off @ $69
LEGO NINJAGO Ultra Stealth Raider 70595 $40 off @ $49
LEGO Star Wars Battle on Scarif - 75171 $24 off @ $55
LEGO Nexo Knights Jestro's Headquarters 70352 $50 off @ $75
LEGO Nexo Knights Clay's Falcon Fighter Blaster 70351 $20 off @ $39
LEGO Super Heroes Batman: Killer Croc Sewer Smash 76055 $36 off @ $89
LEGO Marvel Super Heroes Hulk vs. Red Hulk 76078 $29 off @ $59
LEGO Duplo Town Square 10836 $39 off @ $49
Some TLBM sets are 30% off
Again, ring and check stock level with staff member before heading to store, lots of Brodens knew these deals. I met female Broden in Doncaster who was loading 4 of the Tractors into her trolley, non left on the shelf.
Prepare your 5% off WISH gift card via Cashreward prior to purchase, good luck.