Glaus has a player option for next season, which he may well exercise. but if he does exercise it, he'd actually be taking a pay cut from this season (from $12.5mn this year to $11.25mn next). he may not want to do this, especially if he thinks he could still get a max multi-year contract elsewhere. he's only 31 this year, so it's definitely possible that an AL club which could DH him once or twice a week might offer 3 years @ $12+mn per. the Cards shouldn't match that. if he finishes the season healthy and with the type of numbers that he's on pace for (~ 120 OPS+, 25-30HR), i'd consider it likely that he's gone.
but the in-house 3B options are pretty bleak. Barden and Freese aren't exactly tearing up AAA, and nobody else is even close to MLB-ready. it might only take Wallace a couple of years, but the team seems positioned to contend in '09-'10.
so who's available? the main 3B FAs in '09 (other than Glaus) seem to be Joe Crede, Casey Blake, Dallas McPherson, and Nomar Garciaparra. Nomar shouldn't be considered for obvious reasons, and it definitely seems possible that Blake and/or Crede will be re-signed by their respective clubs. both are solid, if unremarkable, but both are on the wrong side of 30 and have had some injury concerns. they will be the top two non-Glaus options for teams looking to upgrade 3B in the off-season, so they will probably be priced out of the Cards' range anyway.
McPherson, however, is younger than the others (27 this year), is destroying AAA (1.121 OPS with 30 HR already), and has already proved that he is capable of holding his own in the bigs when healthy. he had a back injury that hurt him with the Angels, but he seems to be fully recovered from that. the dude is a monster talent and probably won't cost as much as any of the other options, especially if the Marlins decide to re-sign Cantu. i wanted the Cards to take a flyer on McPherson this past off-season (he ended up signing for less that $0.5mn), and i hope that they have their eye on him for next year. a 2-3 year contract could bridge the gap to Wallace without costing too much cash and subtracting zero prospects. it would be a little bit of a gamble, but i don't think a prohibitive one, and the potential pay-off is huge.
other (realistic) possibilities include going after Andy Marte (if the Tribe re-sign Blake), who will be out of options next year, but his star has certainly faded since '04-'05. the only other FA 3B are guys like Ensberg and Helms who are... uninspiring, to say the least.