I think you would have obtained a copy of the marriage from a parish register or a copy of an Indian registrar marriage. If the marriage was in the overseas section of the GRO index (and if it was not a marriage conducted by an army chaplain or registered with a consul it wouldn't be) then the GRO marriage certificate, knowing the British Library charges, would I expect be the cheaper copy.
The same follows for deaths in India. If the death was registered (army or consul) the death certificate will be with the GRO, but for the burial you would need to search in the British Library indexes. Having said that from the second half of the C19th onwards the information for burials in India almost always included the cause of death and the date.
Regards
Valda