If he can afford to shoot a 300 Weatherby,he can afford more than $300 for a scope.LOL Seriously though,no need to spend an incredible amount but the $400-$500 range would open him up top some better optics.

For a set $300 the best I might think of is a used 3200 or 4200 Bushnell other than the SWFA 6X already mentioned.