If it isn't authenticated, I would probably look to pay no more than $165. I've seen uncerted Jeters, that are signed on the sweetspot, end at around $150-185. If you keep looking you could probably find one uncerted for a very good price with a better signature than this one. Just post a picture and everyone would help I am sure.
If it were me, with this particular ball, I wouldn't pay more than $150 just because there are many chances of finding others but it's up to you. Definitely authentic so it all comes down to price and appeal.