Presumably a camel that anyone wants to ride has been raised and trained properly. That camel is ever going to be ridden, then putting down $400 for a warm body is only the beginning of the investment.
I assume it's mostly meat but have read elsewhere Australia camels are often used for breeding vigour.
On the training. I know more about horses. Where I live in Australia a typical untrained horse will go for about $2-4k and trained it will go from $3k to $10k. Obviously add zeros for special breeds or quality genetics. I cant see camels being too different in ratio of untrained to trained value, even a lower ratio given cheaper labour costs in ME.