If it's not viable for Apple to sell an entry level Mac mini for 499$USD then they wouldn't have it listed on their website.
Apple also does not offer an SSD option for the entry-level Mac mini, putting an artificial cost barrier for users who want an SSD. This situation is similar to only putting powerful GPUs with powerful CPUs in iMacs. Some users might need a powerful CPU only but are forced to buy a useless GPU with their iMac.
I don't care one bit about Apple's expenses, the number of employees, etc. We know from numbers published by Apple that Macs only make roughly 10~12% of their profits, and the Mac mini is probably 10% or less of that number. Apple could sell the entry level Mac mini at cost and it would barely be a rounding error on their balance sheets. But it would also mean more Mac users and more people paying for Apple services (music, cloud storage, switch some of them from Android to iPhone, etc). But for that to happen, they have to be happy with the low-end Mac mini.
As for trying to push potential buyers to higher priced models, surely you realize that it only works on a small percentage of buyers. Being the entry-level model means it's targeting people with less buying power and for them it's either the entry-level Mac mini or a PC. You can't upsell to people who can't afford it.
You just came up with an impossible target cost of 200$USD for the parts of the 500$USD Mac mini when we don't know how much Apple currently pays for the parts.
We do not know the costs of industry standard parts when purchasing at Apple's level. For example, while I was able to find three 128GB SSDs for around 40~60$CAD, we have no idea how much Apple would pay for the same part since they order a few million parts per year. But my search did show that even at retail prices, for a single unit, 128GB SSDs are cheaper than 500GB HDDs. The only thing that changes for Apple is that they would make even more profit for each Mac mini sold instead of only making more profits for the other two models.
There's also components with a completely unknown cost, such as the motherboard, power supply and case since they're all custom-made for Apple. And given the age of the parts used in the Mac mini motherboard, their current cost should be nowhere near the cost in 2014.