Since Fred Wilpon just announced to the world he’s debt-free and ready to spend, well ... here’s a free agent for the taking who could help immediately: The door remains “slightly ajar” for free agent Jose Valverde to join the Mets as their closer, an industry source told The Post. As with the Mets’ pursuit of Michael Bourn, you bet against this actually happening. But this is considerably less complicated than the Bourn endeavor. There’s no draft compensation tied to Valverde, and nowhere as much money as Bourn required to sign; both players are represented by Scott Boras. Valverde, who recorded 35 saves in 2012 and 110 over the past three seasons with Detroit — the most in baseball over that time span — would require just a one-year contract. The Mets intend to start their Grapefruit League season (the opener is Saturday) with their current bullpen construction — Bobby Parnell as closer, Brandon Lyon and Josh Edgin as the primary setup guys and the lower-leverage spots open, with Frank Francisco off the radar as he recovers from offseason right elbow surgery.