I may be very, very late with getting this info but I've been known to be late with almost every thing on a personal & planetary level:)
It seems that UDK can be used freely for developing games & that there are only two limitations: you must pay 99$ when you want to turn your game into commercial product & if your income hits 50.000$ you pay 25% of anything over that amount.
http://www.udk.comhttp://www.udk.com/licensingSo I'm interested to know if any GS user has worked with UDK & what kind of experience was it? Is it easy/hard/extra hard working with this tools, how more complicated/easier is it compared to GS tools?