The average cost for an artifact is 1596 and there are 60 different ones. As such it seems reasonable to assume that for every 95750 artifact points earned you'll get 2 decks. (It's actually better than this since one of the artifacts costs 20000 and you can remove it from the list of options by hitting the button with fewer than 20000 points stored up.
I make 4135 artifact points per hour so I can expect to get 1 deck space every 11.6 hours. Now I just need to figure out how much deck space I need for all the modules in the known universe!