Hi,
Manor is a beautiful place 60 kms from Mumbai on NH 8. They have a lot of economical resorts. You can also try out Daman (150 Kms) and Alibaug. I had arranged for picnics at all these places for 75 of my employees, and it went amazingly well. Personally, I would recommend Manor and Silent Hill/Pooja Farm in Manor. The place is breathtakingly beautiful and unexplored in monsoon, and both the resorts are very well-equipped. Lonavla/Khandala/Matheran, etc., are very clichéd. You can also try Bhimashankar or Harishchandragad if the women are game for a trek.