An individual item, or a collection, is only worth what someone is willing to pay, and the fair market value is whatever a willing buyer and seller can agree on. If the seller wants to hold out for more, it may be a long time, or a VERY long time before finding an eager (or gullible) buyer to meet his price. Or, a “thrifty” buyer may have to look for a long time before finding a seller willing to get rid of his (trash or treasures) at what the buyer offers.
Perhaps a disinterested heir, or buyer of storage units may have one idea on values (whatever they can get) while a collector who patiently acquired individual cartridges (hard to find in their small geographic circle of travel) over a long time may think they are worth more.
To me, the listed items plus 190 more sound like they could be (eventually) retailed for that $300 or more. Certainly not a screaming bargain for someone with thousands of rounds for bin sales, but someone looking to cull the few desirable and maybe a few dozen uncommon rounds can make it break even.
Moral of the story is, collectors should buy stuff for the pleasure it gives them, not as an investment. You may get your money back, make some, or lose some. Hopefully the fun you have doing it all will make the financial cost or profit a minor consideration.