The Marlins are on pace to draw 1.77M this year, which is actually up from last year.
They actually rank a little higher in Fan Cost Index (which is calculated as 4 tickets, 2 beers, 4 sodas, 4 hot dogs, parking, 2 programs and 2 hats or other memorabilia), than you would expect, clocking in at $221.02, ranking #9. This can be found here:
https://www.teammarketing.com/public/uploadedPDFs/2014+mlb+fci.pdf
Which means they will pull in about $98M
gross from gates and concessions this year. That is a healthy estimate, as with about 200K less last year, Bloomberg had them at $77M last year (
http://www.bloomberg.com/infographics/2013-10-23/mlb-team-values.html). But let's work with that.
While tickets are pretty much pure revenue, everything else is not, with margins varying. But let's assume 50% profit (which is more than aggressive, but whatever), once you balance out labor and cost of goods. (It's important here to remember that the teams themselves bid out the concessions and merchandising to outside companies. If you pay $4 for a hot dog that cost $.50, the team does not take $3.50 profit).
Now let's assume Cespedes will cost about $15M on a four or five year deal (which I think is a modest estimate, YMMV). So they need to bring $30M more to gates to cover his deal, each year, over the life of it to break even.
To cover that cost, they would need to sell close to 7K tickets per game more, every game on average for 4-5 years. Which would put them close to 30K per game. Their franchise high since 2001 is 2012 when they averaged 27.4K with a brand new stadium and a bunch of shiny new free agents.
Do you think they are raising attendance that much from one Cuban guy?