Taxi from Barcelona to Madrid round trip

Hi, I am visiting Barcelona end of October and would like to visit Madrid.
Could anyone advise me the price for taxi from Barcelona to Madrid and from Madrid to Barcelona. My flight is from Barcelona and cant change the flight flying from Madrid, so need to return.

I have also seen the price for train and we are two people. I was wondering to pay same amount to taxi, rather than to train. Any help and advise?

Thanks
Naiba