Here are some of the recent bottom six centers traded and their cost:
-Boyle traded to Leafs for a conditional 2nd.
-Filppula traded to Philly for Mark Streit (who was then flipped to Pits for a 4th).
-Ott to Montreal for a 6th.
-Desharnais traded to Edmonton for Davidson.
-Stalberg to Ottawa for a 3rd.
-Fiddler to Nashville for a 4th.
-Shaw to Montreal for two 2nds.
-Eller to Washington for two 2nds.
-Teravainen and Bickell for a 2nd and a 3rd.
I don't see a single bottom six center on that list who was traded for a 1st+.
The bolded were cap moves, not trades. Pittsburgh is not in the position to make such a move, and thus said players (or similar ones) would never be available to them. Using those two as examples is disingenuous.
The DD trade was in part to address a need and in part due to the ED and Edmonton's protected list. If they didn't move him (Davidson) they were going to lose him.
And Stallberg isn't a center, having only taken 13 FOs in the last 4 years.
That leaves Boyle, Ott, Fiddler, Shaw and Eller. Only the latter pair (assuming you see Shaw as a full time C) are legitimate #3Cs, and personally I see Shaw (when he's a C) as something closer to Boyle then Eller.
Obviously, very very obviously our definition of the type of center we need for this team is very very different.
The only player I see in there I would make a deadline deal for is Eller.
I'd pay a steep price for Flippula. The guy even in a down year last year still put up 35 ES points and 42 overall, and is a pass first center, while typically being good on faceoffs and not bad defensively.
Honestly, out of all the guys even conceivably available, Flippula would rank near the top of that list.