The key if you really plan to flip a decent number of bikes is buy in bulk. Buy at least 25ft or better yet 50m rolls of housing and boxes of 100 cables. Cables come in three flavors: Galvanized, galvanized slick, and stainless steel slick. Those are in order of price from lowest to highest. A box of the cheap cables can be found for as little as $50 for 100 cables. The nicer cables are going to run $100+ for a box. With buying in that much bulk of 100 shift and 100 brake (plus maybe 100 MTB brake) cables, and rolls of shift and derailleur housing it does add up fast. But, in the long run it is much cheaper.

I cheat on price because I work at a LBS so I get my stuff at a big shop discount. But, I would look at Niagara and Bike Tools etc. for the best deals.