One words: COSTCO.
That's the only place i buy cards from. They sell them real cheap, $13 for a brick, which is just a bit more than a dollar per deck. I get a brick about every six months (yes, they last that long when you use fanning powder) so that's only $26 on cards per year.
The reason why i only like bikes is because i think other card are a waste of time. I mean, a custom deck is not all that different, it just looks cooler. So i only buy bikes. Sometimes when i visit a magic shop, i will buy some custom decks just for collection, but i'm never obsessed with custom decks. Bikes are cheap and they get the job done.
Bicycles are the standard, have you ever felt Proganda Cards or Split Spades? They feel so much better than bicycles. And they last 2x more.