Regarding Jensens to add to your collection...
1940s-50s have wood base, cast iron engine base, black firebox, dark blue cast iron.
Those with riveted boilers are mostly from the 1930s and can easily go out of your price range.
Jensens have about the most robust construction of all the toy steam engine manufacturers.
If one doesn't work it can almost always be made to work.
These all can usually be bought for 200-500 USD for a nice working example.
If you are lucky enough to find a complete #20 or 20-G for under 500, jump on it before someone else does.
Happy hunting!
Gil