Can't answer your question directly, because different brands will use different dehumidifying units that consume different amounts of electricity. Best thing to do is to check out the ones that fall in your budget range, and get the specs.
Another way of looking at it is :
1. What is your alternative ? Sealed box with silica gel ? Cannot control humidity too well, either not dry enough or too dry.
2. Leave your stuff outside ? Not good as well, in this humidity.
3. Do you need an 80 litre ? A smaller one, for obvious reasons, will be more economical to run, as well as to buy.