The maximum monthly SSDI benefit for 2014 is about $2642. The average monthly SSDI benefit for 2013 was indeed $1146.43 but it's certainly possible that the original poster has a monthly benefit significantly higher than that.
Whether the average monthly SSDI benefit payment would be enough depends on the sale price and the amount of the mortgage loan. There are a number of areas in the United States where the cost of housing is low enough that 31% of $1146 would easily suffice to cover a monthly mortgage payment (including principal, interest, property tax and insurance). If the prospective borrower has funds for a large downpayment, the available options would increase significantly. However, finding a lender who will provide a a smaller mortgage loan can be difficult as the fixed transaction costs make these loans less profitable.
Interestingly enough, there seems to be a significant gender disparity in average monthly SSDI benefit amounts with the average monthly benefit for disabled female workers being consistently (over the past 50 years) less than the average for disabled male workers. In 2013, 4,299,678 women received an average monthly SSDI benefit of $1011.42 each while 4,642,906 men received an average benefit of $1271.46.