Unity3d is a tiny fraction of the cost of any competing engine. Unreal Engine / Farcry start out costing hundreds of thousands of dollars and some studios might even be paying 1m+ for their licenses.
At $1500 a developer (or $4500 if you need iOS + Android licenses), Unity3d is a steal. Plus you can happily develop with the free version until your company is making 6 figures in revs. The free version is lacking some features but until you get really serious about Unity you don't really need it.
Unreal Engine used to be licensed that way, but they've moved to a royalty model that actually makes it pretty cheap for small studios, and free for hobbyists. The current licensing options are,
Non-commercial use: free
Commercial use for in-house applications (e.g. training simulations): $2,500 per-seat
Commercial use for end-user-oriented applications (e.g. game development): $99 plus 25% of royalties above $50,000
Ouch. App stores often take 30%, which means that only 52.5% (0.7*0.75) of what the user pays goes to the developer. That is quite a significant number.
That's UDK though, not the full Unreal Engine. But to be fair UDK is more similar to Unity.
For anything but not-successful games the 25% royalties is going to be a lot more than just $1500-$4500 up front per dev. I'll take the Unity licensing scheme any day of the week.
At $1500 a developer (or $4500 if you need iOS + Android licenses), Unity3d is a steal. Plus you can happily develop with the free version until your company is making 6 figures in revs. The free version is lacking some features but until you get really serious about Unity you don't really need it.