I don't really understand financial fair play so I might be wrong about this, but it seems like PSG is going to have to move Lavezzi (or somebody else) before they can afford to bring in Cech.
EDIT: By the way I love these transfer posts that you do. You do a better job of consolidating the rumors than most of the professional soccer websites.
FFP in summary - a club is not supposed to lose more than 50M Euros in net spending over a 3 year period. This past spring is the first time that these new rules (which have been discussed and were adopted several seasons ago) have actually been applied. Something like 72 clubs throughout Europe were afoul of the rules. Only a few were sanctioned, though, for truly excessive spending - included were Paris St. Germain, Manchester City and Barcelona.
What has happened is that PSG and City are limited in the amount of players they can place on their Champions League squads, with the limit being determined by the gross salary of the players. Barca, for different reasons, have been banned from doing business for either 2 or 3 transfer windows, but it won't take effect until January (after an appeal), due to shenanigans they engaged in regarding improper signings of underage youth players.
Turning back to how they calculate FFP - it is a combination of transfer fees spent plus player salaries (amortized over the life of the contract), offset by TV revenues, shirt sales, ticket revenues, advertising and sponsorships (although they are supposed to be for market value). With a new TV contract for the Premier League and its worldwide popularity, those teams do the most business in merchandise sales and TV revenues.
In Spain, however, TV revenues are not split equally among all the teams in the league. They pay out based on TV appearances, and so Real Madrid and Barcelona get the lions' share of the Spanish TV money, which is beginning to really upset the other Spanish clubs, because it pretty much ensures a duopoly on the Spanish title. Barca and Real Madrid are probably the 2 richest clubs in the world right now, followed by the top several English clubs.
Bayern Munich is by far the richest club in Germany and dominates the Bundesliga. Dortmund has challenged them the last couple years, but the measure of Bayern's financial power is that they publicly recruit players from other German squads for minimal fees, like the Yankees used to raid poorer clubs back in the 1940s and 50s to buy up rising stars.
The Italian league has been in decline for several years now, and has a TV contract that pays only half of what the contract pays in England - kind of like the dynamics behind college sports realignment. Juventus has won 3 straight titles, but they were tainted in a game fixing scandal several years ago. Roma was number 2 last year, but wound up in the lowest seeded pot for the champions league draw because Italian sides have fared so poorly in these competitions ever since Jose Mourinho led Inter Milan to their treble and then left for Real Madrid back in 2010.
"The rich get richer."