If you want to be heard making a prediction about this off-season that’s almost sure to come true, here’s one: There will be more prospect-for-veteran trades than we’ve seen in a long time. The reason is simple. If this year’s market in free agent position players were a grocery store, the stock would consist of one dried-up head of cabbage, two shriveled lemons, a few dusty tins of chicken stew, a couple of loaves of day-old bread, and a few tough-looking cuts of pork labeled as Kobe beef and priced accordingly. It’s the definition of a seller’s market, and any team with wares worth peddling will not only do so but will be able to fetch a great price.

The dozen or so really good players on the market basically break down into three classes. The first consists of Aramis Ramirez; the second comprises Carlos Lee and Alfonso Soriano, quality hitters whose value is more in their durability than in being truly spectacular at the plate; and the third consists of Frank Thomas, Barry Bonds, Mike Piazza, Nomar Garciaparra, and Jim Edmonds, aging stars capable of tremendous performance, but on whom a team can’t truly count.

Ramirez stands apart from the competition mainly by virtue of his age. At 28, he’s right at the height of his prime, the only top free agent of which this can be said. No player is more likely to fetch a price more incommensurate with his value. Ramirez is a very good right-handed hitter with excellent power, who consistently hits .300 BA/.360 OBA/.560 SLG; he rarely strikes out and has remarkable coverage of the plate. The problem with him is he isn’t particularly durable, having averaged 142 games in the last three years, and he’s a truly wretched defender, both in terms of range and of being error prone (his gaffes include having a routine, infield pop-up bounce off his head during a 9th-inning rally and throwing slow rollers 10 feet wide of first base). Factor in that third base is one of the easiest positions at which to find a good player these days — there were a good five better hitters at the hot corner in the National League alone this year —and Ramirez doesn’t look so great as all that.

He’s still a better bet to be worth his contract than Lee or Soriano, left fielders who, like Ramirez, will most likely end up with five-year deals in the $13 million to $15 million a year range and might do better if the right (or wrong) executive happens to be wearing a lampshade on his head on any given day. There’s nothing too bad to say about either man as a player; they’re solid, dependable no. 5 hitters who play every day. And while they have their flaws — Lee consistently slugs .500, which isn’t quite what you want from a power-hitting outfielder, while Soriano’s relatively poor showings in 2004 and 2005 make one think his contract-year success may have been a mirage — there’s no team, save the Yankees (four All-Star outfielders being enough) that wouldn’t gladly take them for next year.

That, of course, is the problem. Lee and Soriano are 30, and while that doesn’t make a huge difference relative to someone Ramirez’s age right now, it will in a few years. In just two years the pair will be a couple of years removed from their prime, likely nursing a few more injuries, with marginally slower bats, while Ramirez will still be in his prime. The aging patterns of 30-year-old left fielders tend not to be pretty as they move into their mid-30s. Both men are quite athletic — Lee is no tank, and consistently steals his dozen or so bases every year, and Soriano is of course the reigning king of the 40/40 season — but betting $75 million or so on continued excellence from them is no wise idea.

This being the top end of the market, those old cans of stew look like about the most tempting items available. Thomas, Garciaparra, Bonds, and Piazza all had big comebacks this year, and the potential to get anything ranging from excellent to near-MVP level production without making a long-term commitment is, rightly, going to look like a good idea to many executives, who will note that Thomas, Garciaparra, and Piazza all helped drive their teams into the playoffs while on relatively cheap one-year contracts. In the abstract, the problem is that in signing one of these players you’re taking a risk that he’ll hit the wall or prove unable to stay on the field — they’re old men, after all. For that reason, you’ll probably see them all go to teams that need to win a couple of bets to make the playoffs, the same as happened last year. Not glamorous, all told, but watch for the blockbuster. Shoppers with money in their pockets don’t settle for what the corner bodega is selling.