I agree. I can find absolutely no scriptural basis for praying to deceased persons. I find no example of anyone in the bible asking the deceased to pray for them.
Some clarification here:
Catholics don't pray TO Mary, they pray THROUGH Mary.
It's DEVOTION not ADORATION.
Statues are reminders not Idols, just as a photo is not a person.
There is one case that is somewhat close to your example; Saul when Samuel was raised up with the witch of En-dor.
1Sa 28:15 Then Samuel said to Saul, "Why have you disturbed me by bringing me up?" And Saul answered, "I am greatly distressed; for the Philistines are waging war against me, and God has departed from me and no longer answers me, either through prophets or by dreams; therefore I have called you, that you may make known to me what I should do."
Technically, Saul never "prayed" to Samuel but he clearly petitioned him for guidance and direction. I should also add it had disasterous results for Saul.