So you'll need regular 'outdoor' rated cable, not (direct) burial. I'm guessing you won't have to run it in conduit either, unless you have critters there that like chewing up cables.
If the eBay cables you have are shielded they should have RJ-45 connectors with metal on the outside. Note that Cat 6 is stiffer than Cat 5 due to the plastic seperator inside which helps prevent internal crosstalk. If you're only going to be using the cable for cams (one cam per cable) you don't really need Cat 6, you could use Cat 5 instead.
Whether you get Cat 5 or Cat 6 be sure to get pure copper (not CCA = Copper Clad Aluminium) and I would get AWG23 or AWG24 (the link from Shockwave199 is pure copper AWG24 so that's fine; actually it's not because it doesn't seem to be outdoor rated).