It's very hard (or next to impossible) to give an estimate, because there are too many factors at play. It's actually all about earning potential one way or the other. Here are some other factors that are very important:
1. Topic - what are the pages about. Pages about different topics have very different earning potential because the products you could promote would be very different. A page about Insurance or Marketing would be more valuable than a page about cat pictures and the difference should be very obvious.
2. Engagement - as you probably know the number of likes is quite easy to manipulate, so it becomes less meaningful. What your pages need to show to be valuable to potential buyers is a lot of fans that are engaging. Your posts need to be reaching a lot of fans and those fans need to be interacting with those posts on regular basis. When you share something needs to get likes, shares and comments and those need to be and look real.
3. Location of the fans - this is something you know already. US fans are much more valuable than Indian fans, because you can make more money off of wealthier people.
4. Past Earnings - this is something that is quite hard to prove to buyers, but is something that is quite important.
5. Actual buyers - your page doesn't really have a market value until there is a flesh-and-blood buyer that's ready to pay for it. So this is something that will have a huge effect on the price - what people are really willing to pay for your particular page with it's topic, engagement, fan base. You cannot get money for it, unless someone agrees that its worth paying for at the particular price.
