The phrase "a substantially cheaper" is correct and usable in written English.
It can be used when comparing prices or costs, indicating that something is significantly less expensive than another option.
Example: "This model offers a substantially cheaper alternative to the previous version, making it more accessible for consumers."
Alternatives: "a significantly lower" or "a markedly less expensive".
But Sovaldi targets a painful and costly disease with a substantially cheaper, safer, and more effective one-time cure.
At least, that's the hope of Redox Power Systems, a startup based in Fulton, Maryland, which plans to offer a substantially cheaper fuel cell next year.
The passive sampling technique combined with multivariate statistical analysis has proved to be a useful approach to assessing groundwater quality, with a substantially cheaper and more effective monitoring design than the more commonly used monitoring methods.
One perceived weakness in Tesla's plans is the relative expense of the Model S. The company may face only limited demand until it comes up with a substantially cheaper car.
The Environmental Protection Agency allowed utilities the flexibility to achieve the reduction goals any way they wanted, and most utilities chose to switch to low-sulfur coal, a substantially cheaper alternative.
It is a person who will not compromise with a substantially cheaper, mildly dated alternative.
Suzuki in India takes back their old cars of any model from the customers, refurbish them and sell these as pre-owned cars at a price substantially cheaper than new models with six months' warrantee in semi urban areas or villages where purchasing capacity of customers is lower and pollution norms are less stringent.
Furthermore, the report calculates the cost of meeting the 2030 goal with a renewables-based system is £663m a year - substantially cheaper than the £1.85bn price tag of a system with CCS-fitted thermal plant - because the cost of new wind power is deemed cheaper than CCS.
That means owning with a mortgage is substantially cheaper than renting from a landlord, where rents take up 34% of the average household's income.
In this holiday resort on the Black Sea, the slightly cheaper tuition fees at 8,000 euros a year, and substantially cheaper living costs, have made coming here an attractive proposition.
"A drone is substantially cheaper than manned aircraft," he said.
