Note that except in one very specific context, the first cited example is not idiomatically acceptable. Normally, the basic construction...
Little do they know X (note "they", not "we")
is only used where X is some "fact" that they don't know - often, the writer/speaker is effectively gloating over their ignorance (that's causing them to make a mistake, which pleases the speaker).
Note that in OP's context, where X = how much the actors charge, this doesn't actually mean the amount the actors charge is unknown. What it means is the amount the actors charge is very high (but "they" don't know that). Compare to exclamatory How kind you are! = You are very kind!
If you think about it, you should therefore realise that this construction doesn't make sense with a first person (singular or plural, I or we) subject and the present tense verb know.
A credible example using a first person subject would require a past tense verb. For example,...
I gave the street beggar £5. Little did I know how much he "earns" by begging. I discovered later that he makes more in one afternoon than I earn for a whole week's work at the factory.
...where obviously the implication is that if I had known how much he was making, I probably wouldn't have given him any money at all.
It might initially seem strange to a non-native speaker, but Little did he know how little I knew! is a perfectly acceptable construction, where the speaker is asserting that she knows very little (but he didn't know that, which was to her advantage).