I don't know if you're new to RVing or not, but I'd check the date code on the "new" spare that just went on. It could be an original, never used tire, that possibly is seven or eight years old and be of questionable value.
I'd suggest checking the date codes on all your tires. If they are all original to the coach, it would be a very good idea to replace all of them.
As for price, I think $100 or so per tire is at the low end, while $500 per tire (assuming you have the normal 225 75 16s) is in the totally absurd range.
