You're going to be challenged finding decent floorstanders for $300/pr. I would watch Newegg.com every day for the next sale on Polk Monitor 70s (you just missed one). I like the Infinity P363 everyone is suggesting a bit better but they are $330
each. If there are any of the discontinued Monitor 70s left in the channel they'll probably go on sale for $170ea (cherry only) one more time between now and Christmas. Or you can get them in black or cherry for $200ea with free shipping at Buy.com. That's a pretty decent speaker for $400/pr.
Alternately you could get him a pair of decent bookshelf speakers like these
Polk Monitor 40s that are on sale for $110/pr, and get him a $190 subwoofer and stay under $300 total. There are a couple of popular subwoofers at that price point but since I haven't heard them I'll leave brand recommendations to others.