300 Diecast Models inherited

Sorry for your loss. Your best return is definitely not selling it all as a lot however that also eliminates the time involved in dealing with them either individually or in groups. Google is your friend and it's worth combing through the collection and see what the value is and be realistic.

Is it possible the boxes are somewhere amongst his items? Most people who collect Diecast understand the box is crucial for getting a return on the investment. However if your FIL just enjoyed them and never worried about monetary gains with them that idea is squashed but it would surprise me that they aren't put away somewhere.....

JW