A few observations of others who've sold collections.

There are basically 3 options,

1) A business or reseller will offer a base price. They typically won't do an inventory and price each item accordingly. They will offer an amount that is much less than the value, maybe $5 a kit? or $20, depends on what kind of kits they are.

This will allow them to make some money on more valuable kits, while maybe lose some money on less valuable kits. It will also take into account the cost of collecting them, sorting them, storing them, placing them online or taking them to shows and basically sell them over the course of a few years.

If you take the valuable kits out of the group, you will get less offered overall, but some will pay more than others for a collection. You might even be able to negotiate a slightly higher amount if you keep the valuable ones as a separate deal, but this doesn't always work. You may even find someone who will do it on commission.

2) Is how you get the most value for some kits. You(or friends) sort and price each item, list on ebay/forums or take to shows and sell them all yourself. This will give you the most money per kit, but will also take time, effort and money to do. In the end, you will most likely still have some kits left that you will end up giving away for peanuts and may or may not come out ahead.

3) Give the lot to a charity/school/friend/your choice or just toss them. Frees up your space and time and doesn't create endless stress and other issues.

None are great options, but it's pretty much how it is, with minor variations.

The simple truth is most modelers are getting older and are thrifty with their money. Finding the right buyer can take a while sometimes.

Good luck!