You are entitled to the duty of care but not to compensation, that's correct.

There is no fixed limit on the duty of care costs. Per the regulation, Turkish is supposed to provide these for you and you shouldn't deal with the payment at all. In practice, especially during large scale cancellations, passengers are asked to pay themselves and then request reimbursement. The cost should be reasonable - no presidential suite at Waldorf Astoria, no bottle of champagne with the dinner - but there's no specific amount.