I stumbled across this 1996 Lexus LS400 in Magnolia, TX for the princely sum of $240. It does have a non-functional window that is stuck down and has missing a title, but the seller claims it runs and drives well.
If nothing else, it could donate it's 1UZ to a platform better suited for the Challenge.
Just a note, the seller was originally asking $600 but seems to want it gone, hence the price drop.