BarnesX.308

So, we're getting a new bow for my son for Christmas. He has been hunting a Barnett Vortex at 42lbs. Over the last few months, he cranked my Mathews down to 55lbs and shoots that pretty well.

He's 5'4 and 140lbs and can easily pull back 50-55lbs. Not sure about draw length, I'll measure his current bow before shopping.

What's a good bow that he can grow into for the $300 neighborhood? And used is an option.

Thanks.