Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
month [mʌnθ] n ме́сяц
every month ка́ждый ме́сяц
300 dollars a month 300 до́лларов в ме́сяц
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.