Hmm, I'd say something was fishy.
Granted, I am not an AR expert by any means, but from what people have told me this doesn't sound quite right. Why? Because the information that was given to me on pre-ban PWA lowers has their price at between $700-800.
Having said that, most will tell you that PWA didn't make entire firearms, just lowers.
In todays market, a post-ban PWA lower (no trigger, stock, etc) is going for around $100. Doing a little math (even shady math), I can come up with around $600-750 for an assembled weapon, depending on who's parts you used.
Based on what you said, I'd look at the serial number. Don't quote me on this, but only serial #'s lower that 32XXX(?) are pre-ban.
I think the serial # on mine is like 1XXXX. ;-)
Regards.....