In chat today, JR said he got the feeling from Armstrong that defense is the priority over offense, and they're still ideally targeting a #2 dman. If that happens, you're going to have to pay that player too. Quality costs. Even with impending RFAs to pay. Would love if it were Kulikov. Realistically, to get him you're having to offer an established winger (Perron, Steen, Stewart) + top prospect (Rattie). If we're dealing with Florida might as well add Weiss for a 2d.
On the Briere thing, there isn't too huge a value difference between Schmaltz alone and Schmaltz plus 2d. 2ds are valuable, yeah, but the Blues have blown a lot of 2ds lately and it hasn't hurt them. Plus the Blues do have a spare one. It would be great if the Flyers would take Schmaltz alone, or if they'd take a 4th. Either way, Schmaltz + 2d is not some huge value package. While the market will be small, Boston is one of the teams who'd likely have interest so it can't be a complete lowball take it or leave it thing.
Affording Briere, I think it'd be a given that McDonald would be gone after the year. Put it this way, if McDonald were willing to sign a 2 year, 5M contract at the end of this year, the Blues probably (though not automatically) would do that, right? Maybe the Blues would feel more comfortable with Briere's health and playoff impact (which is a huge deal for a team needing to win rounds for revenue sake).
Some of the RFA raises are overstated. Stewart and Berglund combined are going to see maybe 2.6M raise over this year, if you guess a ballpark of 4M per for each of them. Shattenkirk probably starts off at 4M (and his salary gradually increases) and Petro probably starts off with a 6.something. It's signing the two defensemen that'll really determine what the Blues can afford. As they enter this contender window, they need to pay for their own salary increases with deeper playoff runs, or else the team will have to sell off some of the more expensive contracts.