The thing is a fair few clubs at this level have small crowds like Crawley but they live to their means and although they don't run massive profits each season but all just stay above the breadline.
Crawley are not like this, they have got promoted by paying inflated signing on fees instead of wages, which was not taken into account with the wage/salary cap.
The last 2 seasons its well documented that they have got around the wage cap by unusual sponsorships deals and signing on fees such as when they signed Sergio Torres for a minimal weekly wage but with an excessive signing on fee and massive transfer fees for the level...getting over the wage cap but still paying him more that others could afford.
This is what is unsustainable and will have to stop, currently it has been got around by the mystery owners investing large sums in one off sponsorship deals, much in the same way that Notts County did a couple of years ago to get around the wage cap.
Some of this is stated in this article from last year addressing some of the financial oddities.
http://www.guardian.co.uk/football/david-conn-inside-sport-blog/2011/feb/18/crawley-town-manchester-united-fa-cup