Imagine everything on earth is smelted down and sold for its raw material. All the iron, copper, gold, silver, diamonds, wood, etc is sold for the current price for such material. Include the whole earth all the way down to the crust. How much US dollars would it be worth? To make things simpler you can break down advance alloys into more basic ones.
It is worth less than the cost to ship it all to the nearest civilization that would find it useful.
Abundance of elements in earth’s crust.
Now just find out their current prices and start multiplying.
I’m sure you don’t want us to do the work for you. 
Note that the Earth is probably worth more than the sum of its raw materials. After all, I don’t pay anything for air, but it is worth enough that I would try to kill you if you attempted to take it away from me.
I could also say that the Earth is worth all the money in the world.
FWIW,
Rob
I’m going to write a number down on a piece of paper, fold it and slide it across the table. If you need financing we can arrange that right here, no problem. Just let us photocopy your identification while you take the planet out for a test drive.
Just like everything else, it’s worth what you can get for it. Since reducing it down to it’s components would destroy your only market then it is worth nothing.
Can we try putting the Earth up on Ebay?
What’s the shipping on that to Alpha Centauri?
If you choose the buy it now option, we’ll throw in the shipping free!
I’d say, at least, $5,000,000.
I think you’re overestimating.
We only sell FOB
But, it’s used!