Depends on the quality.

You could pay excess of $4000 for some sets of Rotiforms.
WORK or Rays Engineering usually $1500-$3000
And ROTA would do the same job for $1000

I'd personally say if he bought 20" Rims from some random Tyre/Rim Shop for $800 they're probably junk and he got what he paid for.
Not to say they're going to break on him.. But they'd be a very low standard of Rim.
Very heavy, high chance of factory defects, etc.