That's what's been reported, and it sounds about right.
The cost of having a coronavirus test at the airport would be about 150 pounds ($195) per person and the passenger would be expected to pay, said Heathrow Airport chief executive John Holland-Kaye.
uk.reuters.com
So, and it's only in the planning stage at the moment, you wouldn't have to take a test, but if you did, and tested negative, and test negative again anywhere from 5 days and upwards later, then you can come out of quarantine early.
If you choose not to be tested, then you're in quarantine for 14 days.
Costs include the test kits, the machines to carry out the tests on and the people to carry out the process. Realistically, it's hard to see those costs coming down below £100 / person.