To be honest, from my limited large lizard experience, if you're looking for something that is guaranteed to be well-tempered, easy to maintain and care for, and easy on the wallet (even though some individual animals are affordable, care/feeding is expensive), you're going to have to make some compromises in your ideals.

My one suggestion: I'm a huge fan of black and white tegus, heck tegus and general, and I wouldn't go any further than good ol' Varnyard Herps Inc. and their extreme giants.

I personally have had about a 50/50 relationship with green iguanas as far as temperament goes, some are just dolls and others are not only willing to inflict serious injury, but WAY more than capable.

Monitors are just needy in general, but very rewarding.