Considering the entire Justin Upton trade hinged on Arizona’s ability to extend Martin Prado‘s contract into his looming free agency, it is somewhat surprising it took this long. The deal is now done, with the Diamondbacks and Martin Prado to agree on a four-year contract extension worth a reported $40 million – $7MM for 2013 and $11MM for 14-16.

The Snakes were raked over the coals for trading Upton and, oddly, savaging after he was out the door. The difference in opinion on the package Arizona actually got compared to the trade to which they agreed with the Mariners (only for Upton to veto) is striking. The prospects in the Marines trade were shinier but Martin Prado is a very good baseball player.

Now he’ll be a very good player for the Diamondbacks for the next four years, three of which seem to come at a tidy price point.

By signing Prado to a four year deal worth $40MM, the Diamondbacks smartly acknowledge that Martin Prado is not the 5 Win beast the Braves got in 2012, when Prado made 111 starts in left field, where his defense wowed UZR and posted a .345 wOBA. There is a much greater chance that Martin Prado will remain an above-average Major Leaguer, posting around 3-4 WAR just as he has the bulk of his career.

With Prado set to earn an arbitration reward in the neighborhood of $7M for 2013, the Arizona Diamondbacks essentially get three free agents seasons from Prado for $33 million – a little bit more than what they gave a much older and worse player in Cody Ross.

While the deal looks like a steal on the surface, Martin Prado’s future is not quite as cut and dried. The Diamondbacks plan to play Prado at third base full time – he has at which he is yet to make 45 starts in a single season.

There is little doubt that Prado can handle the position, but can he handle the rigours of playing third base all year long, day in and day out. Not only is it a significant move up the defensive spectrum, uncommon for a player heading into his age 29 season, but Prado has played more than 150 games in a single season just once in his career. Perhaps calling him injury prone would be dishonest but Prado is no iron man.

Not many players in recent memory made the switch from full time outfielder to full time third baseman. Chone Figgins did, starting 91 games at third in 2007 after starting 93 games in center for the Angels in 2006. Beyond Figgins, there is the example of Miguel Cabrera, who bounced around (lol) from left field to right before settling at third for his final season in Miami. Cabrera’s defensive work at third base could be categorized somewhere between “horrific” and “hey, that could have gone much worse”, though the Tigers wasted little time in moving him across the diamond to first as soon as they could.

Neither Figgins nor Cabrera provide much in the way of fair physical comparisons, though the three men lined up side-by-side would give Goldilocks flashbacks. If anything, it shows it can be done, by wee flyweights and legit heavyweights alike.

The Diamondbacks don’t have to keep Prado at third base forever, as Ken Rosenthal suggested earlier this week. With both Aaron Hill and Jason Kubel heading towards free agency at the end of the 2013 season, Prado could slide back to left field or over the second base if third takes a toll or prospect Matt Davidson forces the issue.

No matter where he plays, Prado’s high-contact gap power and defensive versatility figure to make this deal a good one for the Diamondbacks. He might not get better in Arizona but GM Kevin Towers is willing to bet he won’t get much worse. Sadly, we can say the same thing about the Diamondbacks after this trade and signing. Dammit.