I would suggest you Goa as according to me it's the best but if your budget is limited than Pondicherry is an blessing to be in beautiful beaches, and a heaven for alcoholics and sea food lovers. I think you will get the cheapest alcohol in Pondicherry as compared to the whole India.
Pondicherry will be a great option for a first time solo traveller. I did my first solo trip to Pondi and loved the town and it's colours :) You have many stay and eating options across different budgets. So staying within your budget wouldn't be a problem at all! Happy Solo travelling :)