But 1B of Fielder's caliber are not. While you can get 1B, the production at 1B is the highest out of all 10 positions(including P and DH). To be above average at 1B, you have to be really really good. a .800 OPS just isn't going to cut it. You are going to need a 900+ guy. Fielder is the only guy that fits that mold that is available or will be available in the next few years, sans the uber expensive Pujols.
The thing is the difference between the elite (Pujols) and the very good (Konerko) just isn't that great. I'm only breaking the bank for a guy like Alex Rodriguez when he played SS, or an Ivan Rodrigues (who by the way I feel is one of the all time most underpaid players ever). Someone so elite that the difference between him and #2 is miles. That's just not the case at first base.
Now I realize that a shortage of available guys at first base might cause a higher check, but that isn't the Cubs issue. They aren't that close to overpay for a guy at a plentiful position.
Guys in Fielder's class or above: Texeria, Gonzalez, Konerko (I think I can argue he's close, maybe slightly behind), Berkman, Pujols, Mourneau (when healthy), Votto, Howard
And that doesn't count the guys you might move to 1b to make room for others to play OF/3b positions
If I am the Cubs I am buying pitching and resigning Ramirez (who I think sucks, but that is another thread). I can live with Pena/LeHair (sp)/ Soriano at 1b