What are some good options for high speed light detection (less response time along with sensitivity)?
Any LED also works as photodiode, for exactly the wavelengths it emits.

In your 50 – 100 kHz case, you can simply use any LED. They should be fast enough. This is totally low-tech! Reverse-bias your LED, add a AC-coupling capacitor, and filter appropriately to extract the signals you're interested in.

India is fairly well-equipped with distributors. Most international distributors also deliver there.