We use a few questions and such to stay "tuned in" to our DS.

A few times a week, we ask:
"Did you learn anything new today?"
or
"What's the coolest thing you did in class?"

And comparing what books he wants on his own vs. what books they are doing in school. During story time, questions about the characters and such show whether he is engaged and understanding the material.

Probative stuff like that.

The $$$ sound far out there to me for the basic question you want answered; it doesn't seem like you need a full consult and profile. We were happy to have the school screening, but we also have full time gifted and highly gifted opportunities and it is all well supported. Is there a middle ground where the tester could do an initial screening like CogAT?