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All meat is expensive and eye fillets would probably be a bad choice to consume a kg/da of because of it's high fat content/marbling. Something like rump which is about as lean as chicken breast is a reasonable and economical choice. Coles sells beef mince that's only 5% fat, which is another good choice. However if you wanted to eat 'mince bullshit' with 30% fat that's your choice. Cheap sausage mince is a goo source of this type of mince.
It's not. Go to the butcher and buy in bulk. Get a side of beef, including all the steaks, roasts, mince for under $5kg, you can even ask them to do the low fat mince. Can't even get mince for $5kg normally.