To follow up on the answer Big Uncle gave regarding PPs, you can also buy the PP during the application for a tag process between 1/1 and 3/15 and that PP will go for the following year just like if you bought it during the summer, if you don't draw your first choice unit. If you do draw your first choice, the G&F will refund that PP money because you can't buy a PP in the same year you draw a first choice tag. The site will also gray out on your account and not let you buy the PP during the summer if you drew a first choice tag earlier in the year and some have tried to do that to circumvent the system, but it won't work!
Also, there are very few units that you can draw with no PPs that have very much accessible public land to hunt that holds animals. Unit 23 is one that if you hunt hard in the BLM and also in the WIHA up in the NW corner you have a chance at success, but it's not typical antelope country and you need to be in shape like it's more of a deer or elk hunt than for antelope.