Net54baseball.com Forums - Trouble Valuing Game Used Signed Ball

Hi everyone! This is my first post as I found this site when trying to find the best way to valuate something I'm potentially going to buy. I looked around the site and read the FAQ and I'm not sure if this is the place to post, so if it's in the wrong place, feel free to edit/move it.

I've been talking to a seller on eBay about this item:

http://www.ebay.com/itm/Jake-Arrieta...wAAOSwLnlWmpAi

As a huge Cubs fan, this ball would be wonderful to add to my collection but the seller and I have both admitted to not really being able to come up with a fair price. On one hand, unsigned game used balls from that same game are going for $200 - $250 or so and balls signed by Arrieta usually go for $75 - $100. Then again, none of the other game used balls on eBay are pitches actually thrown by Arrieta, so this one is a bit more unique.

Has anyone ever bought something similar to this that can help me gauge a fair price? It's really tough to find any kind of comps. Thanks for any help you can give! This website is fantastic!