The MSRP for the wimax edition N810 is $479 and wimax chips are supposedly much cheaper than GSM/HSDPA radios. All things considered the price point will probably be around $599.
The 5800 tube has an MSRP of around 279 Euros and that has all the same connectivity as the N79 but a lower spec camera (3.2 mp which I think is fine for 99% of purposes without a xenon flash) and no keyboard.
So it basically comes down to what Nokia want to achieve with the Maemo 5 device. They can aim at a bigger market with a price point of around USD$399 or shoot for the high end market at around USD$650.