One thing to note… That’s a sportsman/cadet chassis not adult sized one.
BRM were a decent chassis. That particular one looks to be from 2001 or prior based on the homologation plate and the diagonal side pod bars.
$400 could be a good deal. $800 is unlikely. It’s almost two decades old and shows signs of neglect. Expect to have to rebuild the brakes (finding seals may be a challenge) and replace some bearings.
Another thing to be aware of… depending on how fussy a track is, they may not permit the older style diagonal side pod setup. Always good to check first.