3000 to Rs. 5000. Both the laptops also come in 13-inch versions with a similar price difference.
The Macbook Air is actually a good Rs. 10,000 lesser than a Windows laptop with similar specs. The screen and the battery life are all that separate these two. Other Windows machines with similar specs are priced far higher than the Sony Vaio Pro. Some of the other Windows makers like Lenovo and Dell should be coming out with competing machines soon, but the price would be similar to the Sony Vaio Pro at best.
For a price-sensitive market like India, this is a radical shift in what Apple has always offered. I'm not going to get into a Mac vs. Windows war here. I find both have their merits and as a gamer, I'd always pick Windows. But there's no doubt that Mac is a more stable operating system, and doesn't slow down with usage like Microsoft's offering.
The larger point, though, is that the argument of a Macbook Air or a similar Windows laptop now no longer includes an "Apple Tax". If anything, a Macbook Air is cheaper.