Use Government (provincial, federal, whatever) meal or hotel allowances as guidelines if doing research is too demanding.
Interesting idea, but the law is even more favourable for passengers: the airline is simply liable for expenses incurred as a result of delay. Period and full stop. There is no expectation nor obligation for the passenger to find the cheapest hotel or restaurant. The airline will be liable as long as the expense is reasonable in the circumstances.
Obviously, when you are stranded, you do not have the time to find the best bargain.