I'd guess that around 300-350 people are in full time employment directly within the Pro League. But there are also stadium security, stadium staff, printers, webmasters, gate people, concession workers, DJs, announcers, medical staff, match commissioners, match officials, maxi & taxi drivers, photographers, journalists, TV crews, sportswear suppliers, local shops who all owe at least part of their income to Pro League.
Then there are around 900 youth players who are kept off the streets by Pro League clubs as well as the youngsters who attend coaching schools and the girls who play in Pro League clubs womens teams.
By the way, national and WI cricket is better supported, but league cricket (which we're comparing the Pro League to) is very poorly supported.