On Diecast Direct, check the "Sale" items - many good buys there.
Try 3000 toys as well.
Stay away from the two (2) Classic Metal Works beverage trucks posted above - the website may be ok for diecast vehicles, but those two models, although listed as O scale, are definitely in the 1/64 scale area.
Finally, and I'm not sure how others feel about this and will probably get some push-back, but IMHO, the primary focus of a model train layout should be the trains, rolling stock, trackage, etc. and, like most other accessories, diecast cars and trucks should enhance, but not be the primary focus of a train layout. Accordingly, I rarely pay a lot for them.
