I'm also often frugal, but this isn't the right place to be frugal.
I spent 5 minutes buffing tire marks off of my friends boat yesterday after we hit a dock-mounted tire while docking in high winds. If you don't mind your boat being covered in black skid marks then they work fine, but if nothing else you'll be paying for it later in buffing compound and wax.
Used fenders are about the same price as used tires. I was offered two free ones on Sunday by one of my dock mates. Even at local used sailing stores you can get them for about $10/ea.
Well you should be glad the tires were there, otherwise you would be spending more than 5 minutes for the repair. As others have mentioned, cover the tires (I have seen old carpet used) to prevent scuff marks. I have 6 used tires sitting in garage- they were free, saved from last tire change- I can get more free from local tire store if needed. Used fenders here in Hawaii are rare, fenders here do not last long and people keep them until they are completely deflated and torn. I saw some used ones (complete with gashes on them) on the local craigs list and they were nearly the cost of new with no warranty- they sold in two days. There are no used boat equipment swap meets here. There are really not many boaters and very few active sailors.