More than once I have been asked how a novice portraitist must decide his prices. I remember I once said: If you don't have any orders you are either too expensive, or you have too little quality and if you have too many commissions, it may be that you are too cheap.
An interesting book that I am currently reading is "The lives of Jan Six", written by the Dutch historian Geert Mak. I do not know if there is an English translation.
Jan Six, the son of a well-to-do merchant family, lived in 17th century Amsterdam. He is portrayed by Rembrandt. One of the most fantastic portraits of the Dutch Golden Age, the work reflects the close friendship between Rembrandt and his patron. The painting is in the private collection of the Six family and still hangs on a wall in the the Six´s family property. The portrait is rarely shown publicly and that is unfortunate. Breathtaking brushwork and bold approach! One of my favourite portraits by Rembrandt.
The book also gives a beautiful picture of Amsterdam, a city at a time of unprecedented growth and wealth. Here the big money was earned and great artists picked their share. If at that time a portraitist in Amsterdam had no jobs it was only due to his quality and not to his price.
See this video about the expansion of the city of Amsterdam in the 17th century. Its explosive growth is like the Dubai of today.