First off, ever wear body armor?
It isn't fun, especially when you don't have a choice, even with wooden substitute SAPI plates.
AR 500 is going to be worse. Yeah, they're heavy. I've used Interceptor Body Armor. Looks cool, weighs a ton, bulky as all get out.
Anything decent won't be even remotely cheap.
Now, I used a Tactical Tailor rifle vest over mine, it worked out pretty decent, have used it alone. Not heavy, had pockets for everything and was about $125-$140. They don't make this model any more, but they do make others.
If plates are required by the rules, that's different, you've got to use them then. But, if they aren't required, you might want to skip them.