Honestly there is no specific scooter for a specific person. And there are different variables, there are custom builds and out of the box completes to choose from, some light some heavy and some in the middle, and of course different price ranges, even more, different sizes of certain parts and different styles of those, if you want a fairly decent complete that costs 300 and lightweight I would suggest this:
http://www.shopmothership.com/products/district-complete-integrated-scooter
or if you want a complete that costs 300 and is a bit heavier for more strength go with something like this:
http://www.warscooters.com/products/lucky-strata-scooter
but there is no set point for a scooter whether it be a complete or built from the ground up, prices even vary between different places and websites, so I suggest not really looking into having people telling your friend what to get, but have your friend, think about the style of park riding he does, and how fast he progresses, how clean he lands tricks, and of course how much he weighs, even though the average complete goes for 220 pounds, the design of the whole complete or even certain parts on it make it vary between each person, so do some studying and check out the specs on certain parts and completes and if there is a certain part you are curious about, look it up to find reviews and such.
and the reason why I am not mentioning a "custom" build is because generally a custom build for a flat 300 is kind of hard to find most of the time