So for Oculus, both Unity and UnrealEngine are free to use up to $100k/company/year and $3k/product/quarter respectively. Beyond that $75/mo or $1500 for Unity or 5% for UE4 seems small enough to just use the product that's better for your use case. Right now UE4 works better with Oculus timewarp feature. The same on Unity5 apparently suffers from jitter.