Must say, it's never crossed my mind for an instant that it was a hoax, but like many others have said here, I now wish it were a hoax - if only because it would mean Kyron is still alive and not being molested somewhere.
It's hard for me to imagine someone doing such a thing and thinking they can get away with it, but some people really are that egotistical and stupid. I have no real sense of the Horman's finances, but it's hard for me to think they are super hard up for cash, owning a mustang and living in Skyline area. They don't seem to be extravagant people (Mustang aside), judging from the clothing the kids wear, and their modest home. Also, Terri is a stay at home mom, which is - let's face it - a luxury these days. If they needed more money, she could try to find a job (although prolly not in teaching as teaching jobs are almost impossible to come by in Oregon right now).
I think for someone to put on that kind of hoax for MONEY, they would have to be broke and with little to no money coming in. Kaine has a good job at Intel; I know that position pays well, so why give that up? If such a hoax were to happen, it would have to be for attention - like the Richard Heene (Balloon Boy Dad). But the Hormans have no noted history of attention-seeking antics.
So I think it's an interesting idea, but can't think of how it fits with this family.