I'm sorry about your house and hope everyone is fine.

No one can guess how much it will cost to rebuild it. First, this will vary tremendously by location. All of the the items that go into a house including flooring, trim, HVAC systems, electrical, etc. will factor into the final cost.

I'm guessing you've already spoke to your insurance company.

So sorry for your home. Hopefully you have talked to your insurance company. First thing you want to know is if you have replacement coverage? There are basically two ways to insure a home, one is where you have a specific dollar amount you insure it for. This is generally based on what you bought it for. The other is replacement coverage, which estimates the cost to rebuild your home and increases your coverage every year.
Aside from that, you say the exterior is fine, but has it been determined to be fine by anyone? Is your home one story or two? Do you need to rebuild stairs? Do you need to replace windows? Where are you located? These will all add to the cost to rebuild. Assuming you have insurance, your insurance agent would be the first one to talk to, and an adjuster would be q great help in giving you an idea what your rebuild may cost.