IMO, the organization needs to stop trading for just AA players. The return for any trade of guys like Santander and Mancini needs to be for major league ready talent.
They could get someone "major league ready" for these guys, but then that player wouldn't be much good. Would be a utility guy or platoon outfielder or maybe a middle reliever. You aren't getting a good, young, fully baked player for 1/2 year of Mancini or even 2.5 years of Santander.
So either take a cheap but low upside major leaguer or go for a minor league guy(s) with more upside but more risk or just don't trade them. There aren't really any other options.