I think you have to differentiate between a train operator/collector who has his or her layout populated with diecast cars and trucks in order to present a more realistic looking layout versus a diecast collector who also happens to have a train layout.
I believe most of us fall into the former category and I have always believed that cars and trucks were meant to enhance the appearance of a layout and not be the centerpiece, which should be the trains. As such, I cannot justify spending a great deal of money on cars and trucks, especially in the smaller (1/43 to 1/50) scales. I would say 95% of mine fall into the under $10 category and the most I have ever spent is $40 for one particular truck.
On the internet sites, I almost always gravitate to the sale/open box items and select from there.
That being said, I can respect full-fledged diecast collectors and what they spend on their collections. There are a lot very nice looking and finely detailed cars and trucks out there, especially in the larger 1/24 and 1/18 scales.
