Something like 9,500 for their opener, according to the story about the Bills players there.
NFLE does not exist to make money. It exists for one reason: so that the NFL can perpetuate the idea in the US that football is going global, that the world thinks football is great, and that rugby - the de facto global 'football' - doesn't exist.
Another example: remember the first exhibition games played in Japan a year or so ago? They made a big deal, frequently repeated in the booth, that they had to play in baseball stadiums because there were no regulation football fields. Funny, but they could have used any of the fields of the professional rugby teams there. But then the announcers would have been talking about rugby in Japan instead of baseball, which is not considered a competing sport.
So why does the NFL do this? Rugby is a big sport internationally, but it's not going to make professional inroads in the US - they've got short-sighted clowns in management/ownership that would make MLB and the NHL blush. However, the NFL didn't get to #1 by being complacent - it thinks very long-term. Part of their strategy against rugby inroads here is discouraging any discussion of rugby. So my theory is that the NFL considers NFLE to be a sort of inexpensive expeditionary force which lets them keep the initiative against world rugby and influence the overseas coverage by american media.
[For what it's worth, Germany is the most successfull country for NFLE. There are several reasons for this, one of which is that in contrast to the UK, France, and Italy, I believe there is no professional rugy played there.]