However when I mine worldcoin on 100 KH/s, for about 1400 minutes (23.33 hours) it only gave me about 25 WDC which is about 0.00275373 BTC at current exchange rate which is about $0.4 at the average rate of $156 / BTC, meaning I do get more than what it says on wheretomine.com So, that would mean that if I was mining that long at 3250 KH/s I would have gotten $0.4 * 32.5 = $13 a day x 30 for 1 month = 390$ x 61.13 for INR = 23140!
I am not taking electricity into account, because in my locality it is dirt cheap
Your calculations are absolutely wrong. And there is not such thing as "dirt cheap" electricity when the income is so low.
Sapphire/Gigabyte are going to be your fastest cards, I do not have experience with MSI but I have heard they are right up there with Sapphire/Gigabyte in performance.
You would be very lucky if you found one for sale new with unlocked voltage. If you don't mind not having a warranty you can get a good 30-40% off of the retail price buying used at auction on ebay and depending on how old the card is you have a better chance at getting one with unlocked voltage.
If you go with MSI get the 2nd one since it has dual fans.