There is no average disability payment you can expect. As an estimate, you could take the median between the highest amount and the least amount. For an example, see below.
Highest Disability Payment: $1,600 per month
Lowest Disability Payment: $600 per month
Therefore, $1,100 is the median amount.
$1,100 is only an estimate. Disability amounts depend on what you paid into the program and how long you worked.