According to an estimate prepared by tickeiQ, playing the 2020 NBA Finals between the Los Angeles Lakers and Miami Heat without fans will have a huge impact ticket market value. The ticket market value losses are projected to exceed $200 million.
That estimate is based on the most recent NBA Finals secondary market value for each team*number of seats*number of games played without fans. This is not a precise measure, but the simplest way to benchmark the magnitude of losses, by team and conference. For the entire NBA Finals, the estimated ticket market value is $212 million.