Hard to say, as I don't pay attention to catalog values once the card is mine. Many of the cards I obtained were once "worth" more, back in the day.
Here are a couple modern cards that once had pretty insane values...
1994 Score R/T September Call-Up Redemption card
1993 Finest Refractor
Probably pale in value comparison, but a seldom seen Joe Montane Rookie item, 1981 MSA disc
Then I have a plethora of older cards that have high BVs, but that doesn't take into consideration current condition. Most of my older cards have some or a fair amount of wear and tear to drop the value enough from BV to make them worth much less than BV would lead you to believe. Cards like...
1952 Topps Andy Pafko (The #1 premium over-exaggerated!!!)
1911 T3 Turkey Red Nap Rucker
1954 Wilson Franks Gil Hodges
1954 Stahl Meyer Duke Snider
1958 Bell Brand Roy Campanella, Reese & Hodges
A pair of Jacks
(1949 Leaf Jackie Robinson & 1949 Bowman Jackie Robinson rookies)
1934 Goudey Lou Gehrig and a ****** Foxx
1951 Topps Connie Mack All Star Christy Mathewson
My mini Zach Wheat collection, including a T204 Ramley and a Cracker Jack
A couple of '56 Topps scrubs!
Those are just a few that I had scanned already. Given condition and values in the book, not sure which I would call my "most expensive". Heck, it might not even be one of these for all I know.