An older player who gets on base and plays solid defense is now-minor-leagure James Loney who was released by the Rays and picked up by the Padres. For my hometown El Paso Chihuahuas he's doing quite well, hitting .333 with a .368 OBP while delivering 2 HRs and 23 RBIs. He's not a power hitter and never will be, but he could be a table setter for the Mets' RBI guys. He'd only cost minimum wage and whatever the Padres would want in return.
The best of the bunch to consider here would be the Brewers' Jonathan Lucroy. He's not a slugger (career high once of 18 HRs) but he is a .280 hitter who doesn't strike out much and can play both positions of need. His contract is not bad at $4 million this year and a $5.25 million option next year. The buyout is just $250K if they choose to go in another direction. The Brewers may harbor some lingering resentment towards the Mets after last year's Carlos Gomez fiasco, but a trade with Kevin Plawecki and a pitcher such as Sean Gilmartin could get that done. There's also the subject of last year's trade -- Zack Wheeler -- who is closer to a productive return than he was at that time. Personally, I'd be reluctant to do that as Gomez was a defensive whiz with power and speed whereas Lucroy is a solid but unspectacular hitter and adequate at best defensively.