You can probably buy 2 or 3 of those Varney/GM/AN 10 wheelers at any of the 2 rail shows any time. Or a 4-4-2 or sometimes a pacific. And the price is generally in 250-300 range for a decent used model and about the same for kit. Althought pristine kits are not as common.
As for a bread and butter loco, the Atlas O SW9 in 2 rail has been around for many years and it is a great model and a good runner.
While it is true that new 2 rail locos are mostly built to order now even by MTH. But they are not longer only high end brass. Sunset and MTH diesels in 2 rail are not brass - most do have brass add on details. Sunset stuff has very good single motor mechs with gear reduction to improve slow speed running and does cost a little more than MTH 2 rail.
Sunset steam does not generally run much more than the high end steam in 3 rail.
Used brass that may be new old stock, at train shows is often cheaper than the new 3 rail stuff. I am referring to the scale models, not the low end toy trains.
As a resource, there is an On-line magazine called "O Scale Resource" that is free to view and focuses on 2 rail scale modeling. It is a good source to describe what is available in 2 rail.
