Goa and many other places in India have gotten a lot cheaper to get to as a result of low cost carriers in India. For airfares on the cheap, Spice, Go and Deccan should be checked out. It will really make a lot of 3 day trips possible and affordable.
I'd suggest a Rajasthan trip (Udaipur, Jaipur, etc.) either early on or late into your stay this time. It could be anywhere from 3 days to a week.
I also suggest Agra and Fatehpur Sikri. Could be done in 1.5 days.