Go for hostels to stay You can use airnb for finding someof them. Eat mostly street food . Get the cheapest flight to go there. Mostly use walking for transportation. You will travel good.
Hey Aditya! Bali is a great place and you get real cheap accommodation. Plus scooter around bali to save some cash. Food out an about bali is not pricy. Alcohol is expensive, so make sure you pre buy from the duty free of your home airport. The place you should be looking into to save money is flights. Book your flights before hand as they can be troublesome. Ive been to Bali this fall and have few blogs on my profile and website. Do check them out ;) happy travels ;) I surely would assist you with anything further.
Aditya, look at this app for flight booking known as Kayak they will give you the best air fares. Keep in mind sometimes you might get a better deal if you book one way tickets to and from the destination rather than a round trip. Check it out, all in all 21,000 sounds good to me for Bali ;)
You can travel to any place easily you plan according to your budget. Bali is such a happening travel destination and has something for every type of traveler. Decorated with mountain and sandy beaches, do visit some amazing places in Bali like Tanah Lot Temple, Bedugul, Nungnung Falls to name a few. You find hotels in Bali here: https://www.tripoto.com/hotels
For cheap accomodation, Go for an AirBnb. They have the best affordable and yet luxurious stays. I stayed at Villa by Santi. For food, there are cafe's in Tegallalang Terraces to sit by or even some shacks around Ubud. For a detailed 6 day plan for Ubud and Gili, you can refer to this article: https://www.tripoto.com/trip/dare-to-not-be-charmed-by-bali-photosabroad-5c38d92578a25