LTD is most often sold as a benefit in group insurance plans. It is also available on an individual basis. One can achieve significant savings in the purchase by extending the waiting period.
The longer you wait before beginning payments, the lower the cost. Don't forget, that most policies coordinate with SS disability payments which can begin after six months.
Another key fact to determine is the "definition of disability" in the policy. Usually, for the first 2 years or so the definition says something about the inability to perform your customary occupation. Some policies change after five years into the "inability to perform any occupation". A little thought can help you understand the complications that this could produce.
When I worked, we had a disability group plan that provided cover after 90 days of disability. The company had a generous sick leave policy and one could accumulate this over the years. They would only pay for a portion of these days upon retirement, but we knew that we could make it to the onset of the LTD cover.
I understand that some companies offer a Short TD cover that begins after 2 week and can carry you to a 90 time.
Occupation make a lot of difference. Prior to carpel tunnel, office workers paid the least, and those in construction often couldn't buy it. I'm out of touch with current underwriting, but most companies that write disability on an individual basis often lose money, especially when the economy is bad.