I've never tried to set up an offline repository before, however I did find a couple pages which might help. While I don't envy you the amount of reading involved, from the look of things you might be able to get a quick and dirty local test repository up and running relatively quickly. It looks like there are also some repository archiving programs which could make this easier for you so you don't have to necessarily manually structure the whole thing.
This one is specific to Ubuntu, but gives you the basic idea of the process and, to my knowledge, there isn't much different as far as apt and dpkg are concerned between Ubuntu and Debian and you can get the proper Debian url's from the other links:
https://help.ubuntu.com/community/Ap...ine/Repository
This one is the Debian document on setting up a repository:
https://wiki.debian.org/HowToSetupADebianRepository
This one is on the format and structure of the repository so clients understand it:
https://wiki.debian.org/RepositoryFormat
Anyway, hope this is helpful.