I live in US and travel to India and South East Asia often.
If you are in India for few days, your best option would be to get a prepaid sim card there.
Airtel is the biggest cellular operator and you can easily get a sim card at any Airtel shop for really cheap (less than US$5). The cellular usage charges are not high in India, but I must warn you that the internet connectivity isn't like what you are used to in US. Cellular internet is mostly 3G and 4G LTE is limited to few cities and that too with spotty coverage. Free WiFi isn't very common and is mostly limited to hotels, so Project Fi isn't a viable option.