claiming GST as a cost

Apologies if this has already been asked and answered. I'm having a discussion with a colleague re claiming of GST on an invoice where the entity has an ABN and is not registered for GST.

If a tax invoice total is $1,100, being $1,000 for the item and $100 GST, does the entity claim (in their tax return) the expenditure amount as $1,100 or $1,000? Is the GST included as expenditure if the entity is not obliged to register for GST (as their income is under $75k)?

Thanks in advance.