For the Bears, the estimated ticket market value loss for games played at 20% capacity would be just under $170 million. If fans aren't allowed to attend games at all, that number jumps to nearly $211 million. For the entire NFL, the estimated ticket market value losses would be $5.6 billion with 20% capacity, and nearly $7 billion if no fans could attend.
Those estimates are based on the secondary market value before the recent announcement*number of seats*number of games played at reduced capacity. This is not a precise measure, but the simplest way to benchmark the magnitude of losses, by team.