Glen I thought you had a ZNA, good luck you won't regret it.
OP I think you are underestimating the cost of producing the high end products, buying materials in small amounts, having machining done in small amounts, labor, most of these guys have a lot more than $40 in their mod that sells for $250. Not to say there are not gougers, the market will correct them.
Heck I think Zen has more than 20 workers, does in house machining and he has said he makes $60 on the $279 ZNA, and I believe him.
And good point on reselling, mid-high end mods hold their value exceptionally well, often selling well used for near or over the purchase price. Try to sell a used TV, diamond ring, or car, be lucky to get half the purchase price.
Ever try to sell a bag of cigarette butts, ash, and empty packs?