[kazinator]

Problem is, I paid a refundable deposit on the bottles, as an incentive for returning them.

If I lose 10 cents by turning a 500 ml bottle into filament, will I get at least 10 cents worth of filament out of it?

[imtringued]

You can probably get 25 cents worth of filament out of a plastic bottle. Most of your savings will come from not having to pay taxes.