Do you use granulated dry bakery yeast or wet molded bakery yeast?
That would be Brewer's yeast, the end result of brewing beer. It's then dried and processed to be used as a supplement for health food advocates. Packaged yeast, the activated kind for making bread, is simply too expensive to use for this.
You might find brewer's yeast as an animal feed, I haven't found a good source and go to the local "muscle building hobby" store (GNC) to get a pound (.9Kg) for around 13 USD.
I haven't needed to put my protein on the bees this year though we've had weather that in more common to Phoenix AZ in the summer. Either they don't like what I've been keeping in the freezer, or they have another source.