Lacus - Technically, selling them above any price isn't really "right", but rarity makes something valuable. Only one per licensed tu-ka dealer, and most of them were likely thrown away once the phone wasn't being pushed anymore. There aren't many of them left, 2000 yen would be a hell of a deal for a dummy. I usually see them go for between 4000 and 10,000 yen (I personally could reasonably be expected to pay about 6,000 yen for one).
Then again, I find officially pressed promos to be extremely valuable, while most people find them worthless (I only find the laser-printed blank cassette and CD-R ones worthless since they're easy to fake, unless they're in special casing or recorded on something like DAT tapes that most normal people don't have... even then I proceed with caution
~). There are alot of things I'd be willing to pay for that people would never touch
Needless to say, a complete set of the actual working A MODEL phone is worth more, since it is functional and, if it has all its pieces, is in perfect condition nearly a decade after its release. But I wouldn't pay more than $200 for the whole thing since it is unusable outside of Japan, has limited functionality compared to modern phones, and outside of big ayu fans there's no demand for it.