The phrase "a very substantial amount" is correct and usable in written English.
It can be used when referring to a large quantity or significant degree of something, often in contexts involving finance, resources, or data.
Example: "The company reported a very substantial amount of revenue growth this quarter, exceeding all expectations."
Alternatives: "a considerable amount" or "a significant amount".
"It's a very substantial amount of money that's been freed up," said Abiel Reinhart, North American economist at JPMorgan Chase.
Last year there was a sense that it was unseemly to be looking at spending a very substantial amount of money on real estate.
"One thing that we weren't going to do was just throw more money at a problem … There was a very substantial amount of money on the table and it's been there a long time.
Additionally, since the exemption amount would be lowered, and there are so many more real estate transactions in the Town of Brookhaven when compared with the five East End towns, a very substantial amount of money would be raised.
He suggested an adjournment of 90 days to allow defense lawyers to look at a "very substantial" amount of evidence and said his office wanted the trial to start within six months.
A key reason for Mr. Romney's low tax rate is that a very substantial amount of his income comes from capital gains – 51 percent in 2011 and 58 percent in 2010.
We observed a low level of DCF signal in the WT retina (Fig. 2A) but very substantial amounts in the Vldlr-/ retina (Fig. 2B).
At that hearing, he hinted at the Treasury's improved forecast for the program, saying "we're going to be able to return very, very substantial amounts of money to address the critical economic needs, long-term fiscal needs, of this country".
The Arcturus amplification procedure was able to produce very substantial amounts of nucleic acids from just 250 pg of total RNA and therefore should be considered more reliable than the other two methods at lower input thresholds.
