After the recruitment of conquered folks in the second year of the war, their forces grew four fold. And all conquered folks were made into Neo-Crusaders. By that time, they had attacked the Republic. Not very likely they were only 50.000 in that time. They made up the majority of Mandalorian forces during the Mandalorian War, and they had become formidable enough to challenge the Republic.
Kandosii-type dreadnaughts carried a maximum of 40.000 troops including the crew. So it's well over that number.
Gratulator's right and if you consider that the mandalorians did a LOT of conscripting whenever they took over a planet, they always bumped the numbers of their forces by at least 4 times more then when they started the campaign. Plus you have to consider the amount of people on a planet WORTH conscripting, because no mando recruiter worth his/her salt would take the elderly and the sick to become a neocrusader.