Royal Ascot prize-money totals will drop by more than half from the forecast figures, with £3,680,000 up for grabs compared to the £8,095,000 announced in December.
The 55% reduction means all races will be run for a minimum of £35,000 rather than £95,000, and the eight group 1s at the expanded meeting will all be worth £250,000.
Ascot, which was set to boost purses by £765,000 compared to 2019, had been planning to run its first two £1 million races at the meeting, with the Prince of Wales's Stakes (G1) and the Diamond Jubilee Stakes (G1) being increased from £750,000 and £600,000, respectively.
Instead, race values have dropped because of the coronavirus pandemic, and the five-day fixture will take place behind closed doors from June 16-20.
Ascot chief executive Guy Henderson said: "This was set to be a landmark year for Royal Ascot prize money. However, these unprecedented times have intervened.
"Some 70% of our annual income comes from public admissions, including hospitality, and producing in excess of £3.5 million in prize money in the current circumstances would not have been possible without the support and commitment of our official partners, QIPCO and Longines."
For this year only, Royal Ascot is being expanded from 30 races to 36, with consolation races for the Royal Hunt Cup and Wokingham, the reintroduction of the Buckingham Palace Stakes, and the creation of three new races: the Copper Horse Stakes, the Palace of Holyroodhouse Stakes, and the Golden Gates Stakes, all of which are worth £35,000.
Henderson said: "We have sought to respond (to the times) by producing an enhanced program of racing this year to maximize opportunities to participate and which in its own way will deliver an exciting and memorable royal meeting."