I just spent over 4 years living in Bangalore and got a few suits made. With the most basic fabrics, you can get one starting around $150, so for $300 to $500 you will be getting their higher end fabrics and very likey a damn nice suit. Biggest advice is to find a good tailor and don't rush the process. I've used a few tailors (mostly for bespoke shirts which you can get starting around $15 for the cheapest fabrics) and some I've loved while others gave a pretty terrible fit. For suits, I've used a shop on Commercial Street but I don't remember the name (there are a million shops there). I have a lot of friends that have used and loved Prakash Tailors which is by Johnson Market, but mostly for casual shirts with more of an Indian style to the fabrics. I did get a suit made by Prakash, but unfortunately I didn't go until right before leaving Bangalore so the process was rushed and I didn't get a chance to pick up the final product (my wife is still there and got it for me).
That leads to my 2nd piece of advice which is to not rush it. Ideally you will go into the shop several times before getting the final product. The first visit you will pick out materials, they will measure you, and you will tell them what type of fit and style you want. Then you will come in a second time, usually after several days to a week and they will have the suit roughly put together in somewhat of an outline. You will try it on and they will use chalk to draw marks and notes for alterations. At this point it resembles more of a bunch of fabric stuck together than a suit, but this visit helps a lot with the overall fit. Then a few days later you will come try on the suit after it has been properly sewn together and actually resembles a suit. At this point you can have minor alterations made to dial in the fit just right. Then it will be another day or few before the final product is ready.
The time is crucial... if you only have 2 or 3 days don't expect an amazing suit without getting very lucky. I made the mistake once to try and get a suit while on a long weekend holiday in Rajastan and ended up rushing the process and having an awkwardly fitting suit that I now never really wear.