PLR-16s go for around $600 at their priciest. You can probably find them for less than $500
They're also much more lightweight than the 556 pistol.
BUT, if the 556 is what you fell in love with, then it's the one you fell in love with. Don't go buying the PLR off of gunbroker until you've handled one for yourself.
You might absolutely HATE the PLR for all any of us know (I think it feels decidedly flimsy compared to the 556 pistol), and this is obviously more a 'cool gun that I like' kind of buy more than it is for any practical reason.
So, if you find a PLR-16, check it out. If you like it as much as the 556, go for it.
If you DON'T, saving up for the 556 might be a better way to go.