People are buying brand new 2013 CBR250R's this spring for as low as $3500 USD, plus TT&L.
And that estimated $5000 USD for a 2015 CBR300R doesn't include the Freight & Set-up charges that many dealers will add on to that price, so it could very well be closer to $5500 USD, plus TT&L by the time you ride away from the dealership.
So you're really talking about a $2000 difference in price between the two bikes... that two grand can buy some really nice riding gear, as well as a few other items that a new sport bike owner will need, such as a rear paddock stand, service manual, engine oil & filters, etc.
Not to mention the fact that no one will be riding any 2015 CBR300R's late summer. Add it all up, and there are actually some very good reasons to buy a CBR250R.