They are even more expensive than average skilled mercenaries.
According to AD & D 1st edition Campaign Set "Forgotten Realms" (P. 61), discontinued in the mid-1360s DR:
The fist is expensive even by mercenary standards, due to its number and the fact that NONE of its front troops have less than the 5th tier. This makes the fist one (sic) incredible weapon on the battlefield, but only to be done by nations or the very, very rich (and very, very angry).
The cost of renting the fist is 10,000 per day plus a share of looting. Since there are approximately 2,000 members, it costs about 5gp per member per day to rent the company. That chronologically later Gold & fame For AD & D 2e (pp. 8-11), which was discontinued in the early 1360s, DR updates its number to 1,600, but it still costs 10,000 gp per day to recruit the entire army, or almost 6gp per member per day.
This figure includes the company's travel and maintenance costs, and we can expect standard-ranked members to be paid less than senior officials. However, this is only the wages you would personally earn if you were a member. In terms of the cost of renting it, Gold & fame notes that hiring a subsection costs a reasonable amount; Hiring 10% of the group would cost 1,000 gp, so the price per man would be the same. You would also expect, as mentioned earlier, to be paid in part of the looting, effectively increasing the total cost.
A considerable amount of time has passed since then, but the group remains largely the same and monetary inflation does not seem to exist. According to the D&D Next Playtest adventure Murder in Baldur's gate, p. 32 (1482 DR):
Aside from tripling its size to almost six thousand members, the mercenary company has not changed significantly since its first few years.
The statistics in this module suggest that the lowest ranked members are below the 4th level. Private and lieutenant ranks are level 1 and 3, respectively. This indicates that much of Faust's current growth has been the recruitment of mercenaries at a lower level. Baldur & # 39; s Gate: Descent into Avernus, p. 162 (under the "The Flaming Fist" section in Baldur's Gate Gazetteer) could be interpreted to support this:
The Flaming Fist offers employment and a sense of belonging to anyone who can raise a sword and follow orders.
However, they are at least trained mercenaries. Descent to Avernus p. 177, table B: residents of the upper town, recommends the extras a knight's block for the officers of the fists and the veterans for their soldiers. This suggests that they are usually well trained and not just a peasant militia. Page 207 states that soldiers have to register for training once a day, which indicates that they are qualified. Page 195, Table H: Outlying City residents, notes that they also have guards, which at least suggests that some subordinate members exist. Tomb of annihilation, p. 199, "Flaming Fist" agrees; A patrol is led by an NPC with the statistics of a knight or veteran with 2d6 guards, an acolyte and a scout.
In the past, all Flaming Fists were elite mercenaries, and hiring them would cost 5 gp per person per day or more. Today, they are more numerous and have recruited fewer exceptional people to fulfill their duty to guard the Baldur Gate. However, there are still many exceptional high-ranking officers, while even the low-ranking members are regularly trained and could be considered qualified mercenaries.