Nishanteeka,
1. Whether you need to buy 6 months insurance or 180 days insurance (or any other duration) depends upon the plan you purchase. Please visit
http://www.insubuy.com/visitorinsurance.jsp and enter the start date and end date and it will automatically the duration correctly for the given plan.
Please note that 6 months can have anywhere from 180 to 184 days, depending upon the time of the year in the calendar. But you don't have to worry about all that. You just put the start and the end date.
2. Most insurance plans start from 12.01 AM Eastern Time. Most of the international flight to Europe/USA leave from India in the early morning like 2 AM, 3 AM and at that time it is still the previous day afternoon here on the East coast. Therefore, in order to cover during the travel time also, please have the effective date one day in advance of the travel date.
3. Of course, best and cheap don't go together most of the times. I recommend that you visit
http://www.insubuy.com/visitorinsurance.jsp, and compare the plans side by side and decide which one would be most suitable for you.
If you have any specific questions, you can of course call us at (866) INSU-BUY and we would be glad to help you select the right plan for your needs.
If you have any other questions, please feel free to contact us at any time.