Maybe gamedev.net or gamasutra.com would have it, I actually remember reading somewhere about their price but I forgot which one's most expensive (plus I dunno if the source was correct).
My *guess*(exp -> least exp):
Q3 -> UT -> Lithtech
Then you have new ones, like I heard Croteam is licensing their Serious Sam engine too... prolly least expensive though
[This message has been edited by BadScript (edited March 04, 2001).]