I am looking for high resolution imagery of the Nicobar Islands. Ideally 3 images (2004, 2005 and 2014/15). My budget is 1500 USD. Which image providers would you advice? Until now I have only worked with free (Landsat) imagery therefore I do not know where to ask.
You are looking to acquire about 2000 square kilometers (based on a quick estimate on google earth) of imagery, at three points in time, for 1500$.
That means, you're looking for data at a price of 0.25$ per square kilometer. Three of the major data providers (DigitalGlobe, Airbus & Blackbridge) all have their lowest price points significantly above that.
You could look into the Indian Remote Sensing (IRS) series, which provides reasonable data at a low price. You can find more information about the IRS series at this site. However, I am uncertain if their data is available at the price point that you are looking for.