It depends on your preferences. but if you are on tight budget you can do a trip within 10k for 3 to 4 days. you can go for hostels instead of hotels and save on stay.
For a budget traveller 10k - 15k can be enough for a 3-4 day trip, if you plan your expenses efficiently. Be choosy while booking your stay. South Goa can offer more budget hotels instead of North Goa. https://www.tripoto.com/goa/tour-packages