What stumps me the most about working out the transfer budget for this close season is the players being linked away.
Xabi. Possibly the biggest fee, but with figures I have seen ranging from 9m to 12m (no sauces, I can't be arsed to find them again) for him, which seem low. Now if Barry is his direct replacement and Xabi does leave, I'm not sure its worth the extra 2m that we could possibly make from selling Xabi for 12m and signing Barry for 10m for example. Which makes me think that either Rafa wants something different to what Xabi offers or Xabi wants to leave for personal reasons.
JP: Again, considering that Valencia is his replacement, the difference between fees mooted is small. The style of play is the biggest difference between the pair, again maybe Rafa wanting something different from a new player. But also with his, the Mancini link (at a proposed 4m) would be a cheaper option than Valencia; in transfer fee anyway, wages would make it about even over a long contract.
Crouch: Most of the talk from Rafa has constantly said that he wants Crouchie to stay. Regardless of a fee. And with very few links being made to new strikers (unless Babel is converted/nemeth promoted) its hard to foresee this sale in terms of helping towards the transfer budget conundrum.
Carson: The most obvious fee and sale. Doesn't need immediately replacing.
JAR: Again the fee wouldn't be huge considering his contract (and lack of ability

) but would need a replacement (one from Arbeloa/ Insua possibly).
Now I know that this list is purely specualtive and working on the thinnest sauce ever spread across a burger... But its point is to draw attention to why some of the players may be released regardless of the money on offer. But then again, it is hard to see the logic in getting rid of JP and Xabi to fund moves for Valencia and Barry per say. In addition possibly. But not specifically instead of, unless Rafa thinks they offer something different to take us forward.
Maybe this does point to a small transfer outlay? Maybe Rafa thinks a little tweak in personel is all required to take us on from 13 draws into four or five draws (for example). I don't know. But they seem the only viable options to me.