There's a zero percent chance I'd have paid for a license if I hadn't been able to try out the free version first. Every major devkit, even CryEngine, has a free license for noncommercial use.
I'd whittled my engine options down to Unity3D and Construct 2 through research, and installed both to determine which would best suit my requirements. As it happens, my first two games will almost certainly be made with Construct, and a much more complicated game (fingers crossed) will be made a year or two from now with Unity, but if Unity had been the only kit I could learn for free, I'd be on a completely different forum right now. =P