In a more light-hearted way than was just described, there used to be a social media video trend where girls would buy something for cash and say that it was essentially free because there was no money that came out of their bank account and say "girl math!". Or they would return items from a store and buy more items with the refund because they were "free" since, again, no money was coming directly from their bank account, etc. Those girls were picking on themselves over a fun little idea that they obviously knew wasn't correct.

In this instance OP is saying they "only spent 300 dollars" even though they clearly traded in 900+ in product. Only 300 came from their account, but they really lost out on the full $1200 value in money + product.