Below the centrally-contracted players, cricket is really semi-professional. The retainers for most domestic players are somewhere between ten and twenty thousand a year, I believe. A player who plays pretty much every game over the course of the summer might double that in match fees. There are also only 12 contracts handed out by each province, so several players only earn match fees. The reason they even get that much money is because most, if not all of it, comes from the TV revenue NZC collects from Blackcaps games and ICC tournaments. Aren't Super Rugby salaries basically also paid for out of All Blacks revenue?
In the end, professionalism (to whatever degree) is sustainable because the national teams make the governing bodies a lot of money, and to keep the national teams at that level, they're willing to basically pay every player at the top domestic level. Because the All Blacks are the biggest draw card in world rugby, and NZC has gone along with the Australian, English, and Indian takeover of the ICC, paying players probably isn't going to be a big problem in the near future.