I do not recommend any fish in a scape-less tank. They need to have a hiding spot, a place to retreat to, or they won't feel safe. The dimensions you use, are those in meters? (72" x 23"x23" then? or 165gal?) I think that the water volume is sufficient for a fahaka - but not an mbu. They require much higher water volume. This brings me back to the decor, fahakas love places to hide. If my fahaka feels like he does not have adequate hiding, he is very stressed and jumpy.... (Stressed: spotty coloring, fidgety, breathing hard, tries to hide, very aggressive. Jumpy: freaks out and tries to jump out of the tank, running into walls of the tank or into glass topper.) By giving one hiding spot, he probably won't be out much at all - he'll hide a lot. If he has a more complex environment that he can explore, with plenty of hiding spots he'll actually be out more (he'll feel safer.) My Fahaka is always out taking a 'stroll' now that I have lots of hiding spots, and open swim waters. He's out more now that he feels he has plenty of options to retreat
As for prices, I think their size influences their pricing greatly. As a baby, my fahaka's book price at my LFS was $23. I've seen pricing close to this on some sites, however I've seen much larger fahakas (8-10") for around $150. As fast as they grow, I'd not waste the money on a larger one, and just get a baby.
I think my Fahaka is easily cared for, but I've never owned an arowana or a clown loach. Fahaka's can live into their teens if properly cared for, and has had ich once - easily treated and gotten rid of. He came with IPs and with proper medication, was eradicated. I've had no issues since, and has been the most rewarding fish I've ever owned.