^--- Do you belive everything the Discovery Channel or Nat Geo puts out? If so, you'd have long since decided that all preppers are crazy.
OT: If you're looking at body armor, don't go cheap. That said, the prices aren't that bad. Ebay has a ton of SAPI and ESAPI plates for decent prices, ie, couple hundred for a set. A vest and soft armor will cost more, but honestly body armor is not something you want to go cheap on. Cheap will equal at least one of two things: more weight, or much lower quality. Neither is good.
As for rifle plates being useless after a few rounds, that's not exactly true. I can't find the video they do with .308, but this video shows the testing with 5.56, and it wasn't until two rounds landed on top of each over that they had penetration: