I've not seen any 5e that's 23 AWG. Maybe it exists. Most cat 6 is 23 AWG, but you have to verify that, and make sure it's solid copper, not CCA. In reality, you'll probably not see any performance difference between 23 and 24 AWG, but for a run that long I wouldn't even consider not using 23 AWG cat6. You can calculate the POE power drop if you want to with each gauge, but with the cameras being pretty tolerant of the POE voltage I'd guess the only difference would be you heat up the wire a wee bit more with 24 AWG. With your run length at the outer limit of the specs, cat6 will give better odds of good data transmission. I'm surprised at the $100 price difference, assuming you're going to use CMR cable. At monoprice today, a 500 foot length of cat6 23 AWG CMR solid copper is $90.