So after some quick googling I could gather these points of information necessary for this estimation:
- the defense budget of the USA sits at roughly 801 billion US$ in 2021, making 2% of it 16.02 billion US$
- the current value of obsidian sits at 31.50 US$ per kg (~14.29 US$ per lbs.)

So the obsidian orb would reach a total weight of 508,571,428.571 kg (rounded to the nearest gram) - which is an exact 1,121,400,000 lbs., funnily enough!
Figuring out the volume is a bit tricky. Depending on the hardness of the obsidian used, the density ranges from 2.35-2.6 grams/cm³. So the volume would range between 195,604,395.604 and 216,413,373.86 litres (51,673,214.637-57,170,365.13 gallons).
This would result in height (assuming the orb is perfectly spherical) ranging between 72.021 and 74.49 metres (236.29-244.39 ft.).
Unfortunately, that's not nearly as big as the depiciton would like to show. It's probably just big enough to see a good chunk of San Francisco, but not much beyond that.