A lot of your pricing questions will depend on the medical specialty, resident state, age and could even be impacted by current health. For example, people who are overweight may be required to pay higher premiums to adjust for the higher risk.
The benefit of locking in a lower rate now is that you will pay a smaller amount on that specific amount of coverage for the rest of your career (provided you buy a non-cancellable policy). This is not an exact percentage however, like you are assuming. I would say on average the cost of disability insurance increases approximately 3-4% each year. For example, $1,000 annually at age 30 - $1,040 at age 31 - $1,081 at age 32 - $1,123 at age 33, and so on. Therefore, you are able to lock in the lower rate without incurring an increase on that select benefit amount.
For the future, you want to make sure you include a specific provision called a future increase option or future purchase option each insurance carrier has a different name for it. The basis is that this provision allows you to increase the benefit amount, at a future date, without requiring medical screening again. The pricing will be based on the attained age, so you will be paying a higher marginal cost on the additional benefits purchased. However, the original benefit amount you purchased will remain at the same cost.
Speaking of discounts though, there may be a discount program set up at your school which would allow for a specific discount, such as 10%, or 15%. Each carrier is different with respect to discounts. The other option is to set up your own discount plan, if you have enough colleagues interested.
Does that help?
