$500 bucks.
If there's rock solid provenance this was actually a display flag at Foxboro in 2001, (honestly, looks like a pretty generic, medium sized flag to me), maybe $750 bucks with that already crappy looking, apparently recent signature on it.
There's nothing historic about it.
This one of one claim is complete speculation and nonsense. I once had a guy try and sell me a Joe Frazier autograph on an airline ticket for a ridiculous asking price, because he said it was the only known signed airline ticket by Joe Frazier. A 1 of 1, you could say.
This was when Frazier signed 8x10's retailed for about $25-30 bucks or so.
I had to hold my tongue to keep from blurting out "So What!".
Everybody thinks their stuff is worth a million bucks, until they actually go and try to sell it.