Wow! Nice pick-up!
I've been to that show a number of times and there haven't been any scarce backs like that when I've been there! I think your timing was just right.
If I were in the same situation, I would have paid the additional $300 for the PSA 2 Kroh in a heartbeat. You won't regret it. Plus, if you ever decide to sell it, the Cubbie is going to be more far more desirable than the minor leaguer. The Cubs cards are generally pretty popular with collectors (with the exception of Tony quinnsryche, of course).
Congrats! Glad there was a happy ending to your story.