Denbighshire County Council is under fire for spending almost £2m a year on just one child in care.
Clwyd West MS Darren Millar has asked the Auditor General for Wales to investigate.
Residents are concerned about the excessive cost, especially with public services being cut.
Mr. Millar wants urgent answers on why so much is being spent and hopes for full transparency in the review.
His letter to the Auditor General states: “The information in the article suggests that the costs of care for a child for which Denbighshire County Council is responsible are just shy of £2m per annum.
“Since the publication of the article, I have been contacted by a number of concerned constituents who feel that such costs cannot be justified and require external investigation.
“Given the above, I would be most grateful if you could consider conducting a review of this expenditure to determine whether it represents value for money for the Welsh taxpayer.”
Darren said: “We are seeing services in Denbighshire being cut left, right and centre so I am not surprised that residents are bewildered by this extortionate spend on just one child.
“Whilst I appreciate there are children with very special needs who demand 24/7 care, and I am not saying they shouldn’t be receiving this help, when you are talking of figures just short of £2m a year, people rightly want to know why it is costing so much.
“I have therefore asked the Auditor General to investigate the matter and hopefully he can provide the answers to our questions.
“This is an excessive amount and given the financial struggles of the council, which have resulted in vital services being slashed, it is only right that we have complete transparency regarding this spend.
“I look forward to receiving a response from the Auditor General.”