The Rangers gave up Justin Smoak for Cliff Lee, and Lee pushed them over the edge to get to the World Series. The Rangers did this with the knowledge that they couldn't resign him. Reyes is looking at a similar WAR as Lee had last year. The Red Sox gave three of their top five prospects for a year of A-gon. The Brewers gave Matt Laporta for Sabathia... well, back when Laporta was a blue chip.
Reyes nets two 1st round picks in next year's draft too, so whoever gets him gets that value too.