Inexpensive way to get replacement donut tire or similar (Saturn S)

I currently cannot afford to replace my normal tire (Saturn S series <2002) and have been riding on the donut tire for several weeks so far. I only need to travel less than 10-15 miles in a week (visiting a family member) so it's not getting lots of use.

Any tips on how to get another one since they would be an affordable way to get months of drive time? I'm hoping for something cheaper than the $80+ I see online. Is there a known inexpensive site or something more like <$50 that could be used for a few months?

Thank you!