Disability insurance is sold in $100 monthly increments, and if you have to collect it, you won't pay income tax or social security on it. This means that you need less than your current gross.
It is generally less available to those whose occupations involve physical work, such as self-employed carpenters etc. These folks are rated as less desirable, and pay much more.
Generally, you have to be healthy to buy it.
The key to affordable coverage is getting a longer waiting period before you can collect. I think waiting periods can go from two weeks to six months. If you have a suitable emergency fund, a 90-day waiting period would be best.
Also important is the definition of disability in the policy. This can be either inability to perform your existing occupation, or any occupation. Policies can contain both definitions with the first appliying to the earliest time of disability, and the second applying after perhaps two years.
Policies are cheaper if they coordinate with Social Security, meaning they pay up to the limit after SS has been deducted. For many people, this means that the private policy will pay zero after SS.
Many life insurance companies don't write it, but if the company is a larger co. and writes it in your state, then you shouldn't worry about solvency. By all means get several quotes to get the best deal.