UDK is $19/month plus a royalty equal to 5% of gross sales (as in, before Apple or Google's 30% or other expenses). This means the UDK becomes more expensive if your game has more than a few hundred $$$ in sales.
Cryengine will be $10/month with no royalties, but does not currently support mobile platforms.
If you are looking at Unity Pro ($1500), and want to publish on iOS ($1500), and Android ($1500) it will cost $4500. You'd need to gross more than $90,000 on your app for the 5% royalty to be more than $4500, and I'd bet a vast majority Unity make much less than that.
Majority of games never break even, and that's ok: it's a high-risk, high-reward business. $90k isn't even close to an adequate 3d mobile game budget of average+ quality, so if you gross so little , you're fucked anyway, or you never had a serious product at your hands to begin with.
Cryengine will be $10/month with no royalties, but does not currently support mobile platforms.