What is a best budget for solo Goa trip ?

My suggestion would be to go for shacks near the beach. They are near the beach, cheap, and there isn't any restriction so no problem on the alcohol scene. A budget of 7-9k should be fine, but it eventually depends on your standards. If you want to eat at expensive restaurants and live in a luxury resort, I suggest you carry a credit card. If that isn't the case, carry 10k with yourself. Have a great vacation!