Irrespective of the price... I like peace in my aquarium....
It is also nice to have something else and not just one fish...
The only SA Chidlids I would consider are severums and geos... they will not hurt any arowana... as long as arowana doesnt hurt them you fine.
If you have substrate in your tank, geos do an excellent job of moving it around and not allow pockets of bacteria to form
The rays are also a good combo if they grow up from small with the aros and to my amazement clown loaches make good colourfull tanks mates