This is an image of some "Hurdy-Gurdy Girls" from J. Ross Browne's article in Harper's Weekly, an illustration from his second trip to Virginia City, Nevada (1863). The women have facial characteristics that were part of an anti-Irish stereotype; a bit ironic since Browne was Dublin-born, but he was protestant and the women in his depiction are certainly to be regarded as poor Catholics. That's beside the point, but I put that out there for context.

It is not clear whether these dance-hall women were engaged in sexual commerce by our definition and understanding. That said, any women who would dance in revealing costumes for money had already entered the arena of sexual commerce by the standards of the day. They may have retained some personal "standard" and not have had sex with customers, but they were already scandalous - and many people in the community would have assumed that they turned tricks at least on occasion.

Despite their frowned-upon careers and bad reputations, dance hall girls were not likely to have frequently engaged in sex for money. (They were called hurdy-gurdy girls because the hurdy-gurdy was an easily transported, one-man band, so it could be taken anywhere.) Prostitutes were clearly understood as such, and these dancing women were clearly attempting to draw a line that meant something from at least their point of view. Their occupation was also safer when compared to the women "on the line."

Hurdy-Gurdy girls would "make the circuit" performing in frontier towns, pick up money, and then frequently moving on. Unlike prostitutes who typically waited until a boomtown was a sure thing before relocating there, hurdy-gurdy girls were more mobile and exploited male-dominated boomtowns where they could pick up some cash for dancing and showing a little skin before moving on.

In answer to your question, these dancing women were common enough, although they were probably more common in young towns. As mining camps matured, the towns either disappeared or they continued to thrive; if the latter, real prostitutes began arriving as did more "respectable" women, so there was less market for the specialist who only danced and then moved on.

There are numerous descriptions of prostitutes hosting "balls" where they would dance with patrons, no doubt with the hope of luring them into a business transaction. This is a different phenomenon since these women were not known to be dancers; it was just a ploy.

In addition, some hurdy-gurdy girls did dance with customers for a fee, but sometimes they only performed, dancing as a "troupe."

I think that answers your questions; I hope that helps.

Richard Thomas Wright writes of Hurdy Gurdy Girls in his book "Discover Barkerville - a gold rush adventure." His book is about the gold rush town that came into being in 1862. This is what he writes

Dutch and German girls were brought in to dance in the saloons. Each dance cost $1.00 and the girls got a portion of the money made from the drinks miners bought them. The were called the "Hurdy Gurdy Girls." They were quite unattractive and often heavy but we're well loved and respected by the lonely miners. They were not prostitutes and did not delve in the trade.

In 1862 an article in the Colonist said that there were just 9 prostitutes in Barkerville, a town of some 5,000 men. The article says "They dress in male attire and swagger through the saloons and mining camps with cigars or huge qwids of tobacco in their mouths, cursing and swearing and look like anything but the angels in petticoats heaven intended they should be. Each has a revolver or Bowie knife attached to her waist, and it is quite a common occurrence to see one or more women dressed in male attire playing poker in the saloons, or drinking whiskey at the bars. They are a degraded set, and all the good men in the vicinity wish them hundreds of miles away."