Yeah only reason im not using Unity3D is pro license is too expensive and you really need it to do much.
So we went with Torque3D (new one comming soon), as pro license costed us 505 us$ vs Unity3D 1500 us$.
And we have source for Torque3D

always a great +
So basicly
Want a engine to make a game without programming at a higher cost, thought a bit limited, use Unity3D.
Want a engine to make games, where you have to do programming, no limits, and full source, cheap, use Torque3D.