Someday soon, spending a day at the ballpark will be the equivalent of yachting, playing croquet or pitching darts on the lawn of the family compound, an ultra-costly diversion enjoyed by the rich and privileged, fantasized about by the rest of us.

In fact, that day may be only months away.

They are building two new ballparks in New York, ballparks that will be as exclusive as country clubs.

One of them, the new Yankee Stadium, makes no bones about what it is, a playground and meeting spot for those who demand the finest this town has to offer, and are willing to pay for it. The other, Citi Field, cloaks itself in the skin of Ebbets Field, the ultimate blue-collar ballpark, while concealing the insides of Madison Square Garden, once the most exclusive sports bar in New York City.

Last week, a two-page letter went out to some 25,000 Mets ticket holders. It thanked the recipient for buying season tickets for the 2008 season. It extended an invitation to renew for 2009, “our Inaugural Season at Citi Field.”

And it issued an ultimatum:

“To secure your seats for Citi Field, you must remit the required nonrefundable 10-percent seat deposit by Friday, August 1.”

The second page was an invoice – for prices nearly double what fans paid this year for tickets to Shea Stadium, hardly a bargain to begin with.

One guy I know got a bill last week – 10 seats to all 81 home games – for $129,600, a whopping 71 percent increase over the $75,763 he paid for the same number of seats for the same number of games this year at Shea.

The man is an insurance broker who uses his seats as an adjunct office to woo and entertain clients. To him, the hefty outlay is a necessary cost of doing business. No need to throw him a pity party here.

In this town, there are plenty more like him and they will buy up every available seat, suite and luxury box in both parks.

But what about the millions of Mets fans who are also true New Yorkers, only less fortunate? The ones who not only can’t afford a season ticket, but couldn’t swing the 10 percent deposit? And what about the working father who on the spur of the-moment on a fine summer night feels like taking his kids to a ballgame?

Come Opening Day 2009, there will be some 15,000 fewer available seats on a daily basis, or nearly 2.5 million over the course of a season, because of the drastically reduced seating capacities at both parks. And most of those seats will either be spoken for, or priced so prohibitively only the rich will be able to afford them anyway.

Both the Yankees and Mets promise a number of “affordable” seats. Dave Howard says Citi Field will have 350,000 seats “in the $12-$15 range,” which works out to about 4,000 per game.

As you can imagine, those 4,000 seats will be in demand.

Those are the people who bring knowledge and excitement to the park. Those are the people who cherish the memories of their first games and pass those moments along to their children and grandchildren. Those are the people, of course, upon which a loyal fan base is built.

Those are the people who will be missing from Citi Field and the new Yankee Stadium.

Someday soon, those parks will be filled and at the same time empty, flush with cash and devoid of soul.