The Diccionario panhispánico de dudas does not offer a suggestion regarding the use of cómo to ask for the price of something (item, service, or currency). I am familiar with the variants ¿a cómo ...
What is the most idiomatic translation of "how often" into Spanish in questions like: How often do the buses stop here? How often does it rain in November? How often do you get headaches? How often ...