There are many good options like
1.Contact eBay's Powership team at first 🙂
2.DTDC Plus not Lite/Green. Plus guarantees the next day delivery to any serviceable location with special packaging.
3.My personal Favorite "Fedex Overnight Priority".
4.Bluedart Domestic Priority. But they will charge more as compared to above three.
Never use DTDC Lite,Trackon,Professional,On Dot or any other cheap LPs for shipping your items which as you are saying is of above 18500. I have never used Indian Post so i don't have any idea of the same. But as far as i know ,they are really slow in delivering. 😛