TL;DR: A single common car might sell for a few dollars on its own. The same car inside a hundred-car mixed lot travels for a small fraction of that, because the buyer is buying bulk. The value in most large collections is not spread evenly across it - it is concentrated in a handful of pieces, and finding those is the part worth doing carefully.
The arithmetic that does not work
The instinct with a big collection is reasonable: look up one car, see a few dollars, multiply by how many you have. Three hundred cars, a few dollars each, and the number looks substantial.
It does not survive contact with how collections actually sell.
Go to eBay, search for a lot of fifty or a hundred loose common cars, and filter to Sold items. You are not looking at asking prices - you are looking at what people actually paid. Divide the price by the number of cars in the lot. The per-car figure that comes back is startlingly small, and it is consistent enough across different lot sizes that it is clearly the market rather than a fluke.
Do that check before you trust anyone's number, including ours.
Why bulk sells for so much less
Nobody buys a lot to own one car. A bulk buyer is buying inventory, a project, or a gift for a child who likes cars. They are not paying a collector price for any individual piece in it, and they will not.
The work does not shrink. Listing one car and listing fifty cars as one lot take roughly the same effort - but listing fifty cars individually takes fifty times the photographing, writing, pricing, packing and answering questions. At a few minutes each, a three-hundred-car collection is weeks of work. That labour is real whether it is us doing it or you.
Small orders are the worst-served. Marketplace fees are not purely a percentage; there is a fixed component per order. On a cheap order that fixed part is proportionally large, so the smaller the sale, the bigger the bite. Selling three hundred cars one at a time means paying that fixed cost three hundred times.
Weight costs money. Fifty loose cars is a heavy parcel. Postage on a bulk lot is a real number, and it is charged against a sale price that is already low.
Not everything sells. Common cars in bulk are not scarce. Some lots sit. A collection's value has to account for the portion that does not move at the first price.
Where the money actually is
Here is the part that matters to you, and it is the opposite of discouraging.
In most large die-cast collections, a large majority of the pieces are ordinary and a small minority carries most of the value. Treasure Hunts and Super Treasure Hunts, Red Line Club cars, convention and event exclusives, genuinely old cars in good condition, error and variation cars, premium lines with rubber tyres and metal bases - these do not behave like the bulk at all. They are researched and sold individually, and they can be worth more than hundreds of common cars put together.
So the honest description of a big collection is usually two numbers, not one: a bulk figure for the ordinary majority, and an individual figure for the pieces that deserve their own research. Anyone who gives you a single per-car number for the whole thing is either guessing or has not looked.
What this means for you
Do not catalogue all three hundred. It is days of work and it will not change the outcome for the common portion. We do not need it.
Do photograph the whole collection. A few wide shots that show the real quantity, the containers and the general condition tell us more than a hundred close-ups of individual cars.
Do pull out anything that looks different. Cars with rubber tyres, cars still sealed on their card, anything that says Treasure Hunt, anything obviously old, anything that looks unusual next to the rest. Photograph those individually. That handful is worth real attention.
Do check the sold prices yourself. Not the asking prices - the completed sales. If a number we give you does not match what you find, ask us about it. We would rather explain the gap than have you wonder.
Why we price it this way
We sell this category ourselves, so the figures behind our offers come from completed sales and from what our own listings actually realize - not from what other sellers are hoping for. When we look at a collection we are working out what it will genuinely sell for, in the format it will genuinely sell in, minus the costs of getting it there.
That is a less flattering number than the multiply-it-out version. It is also the one that survives contact with the market, and it is the one we are willing to put money behind.