Best speakers for $300/pr

I'd make a bid on these Silverline Minuets that are far more than decent...
https://www.ebay.com/itm/253891672222?ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F7...

Or if he prefers to buy new, these Aperions are very decent and a good value as they're on sale and sold direct...
https://www.aperionaudio.com/collections/intimus-speakers/products/intimus-5b-bookshelf-speaker-pair...

Maybe have @grannyring make him some Dueland speaker cables and interconnects if he needs decent wires too. 

Best of luck. 

The Ascend Acoustics CBM-170 is <$350 shipped and is pretty much unmatched for the price.

I recently purchased LSA .5 monitors for $400 (new) and could not be happier. They easily bettered my Maggie MG12s in terms of tone and inner detail.

Hands down Paradigm Monitor SE Atoms.  Go audition them and I dare you to disagree.

Get a pair of Spica TC-50s.