Chuck, a ball like that would only be worth the value of a "game used" auto ball pretty much... you may get a little more being that game, but not nessecarally, and not much, and heres why...

as you know, many balls are used in games, fouls, scrapes, fans snatching them, ect... so theres already a ton of balls used during the no hitter... a home run ball, is completely different.. because theres only 1 ball.. and if it comes at a point in MLB history, it makes it worth even more, like the Bonds and McGwire balls... McGwires sold for 3.2 million if i remember right when he hit the 72, and Bonds was something like 400k for both the 756, 762 HR balls, and the 73 homer year as well, cant remember.. they also arent signed...

theres only 1 of those balls tho, vs many used by a pitcher... the last ball that Felix threw, touched, ect, is probably going to be worth a bit more than just one ball from that game, but the problem with that is, its likely sitting in his house, and you nor i will ever own it, let alone see it in person... he doesnt need the money, and he threw a no hitter while playing for the damn Mariners, id keep it too, i mean its the Mariners for cryin out loud...

but, like you said, something is only worth what someone is willing to pay for it.. my dad beat that into my head at a very young age, so i never got dissapointed when a shop owner gave me 15 bucks for a card that booked at 25, because 1, they had to make money, and 2, a book isnt someone paying for it....

the Bonds and McGwire balls are worth considerably less now, after the fiascos and such, but still would command quite a bit of money, but no where near what they sold for back then...