junk-boxing it

Not necessarily random, but yes, buy some used ones on that kind of budget. Don't forget a transformer though.

weather at a show, or a store, I hit the junk boxes first. items range from complete ready to run trains to bust, rusted items missing parts. I look for re-builders, parts.and the items are usually cheap.

You live near Dale's Train station? WOW, you are so lucky! I went to Dale's back in 2013 on a trip to Virginia Beach, I spent hours there just looking at the items in the glass cases!

Unless you are very familiar with working on 110V appliances, I would not recommend purchasing a transformer that is in need of repair.
In my area, the prices of a 1033 / 1044 transformer that has already been serviced vary from around $25 to $40. I suggest you purchase yours from someone who will stand behind it. Some stores and train show vendors will, others sell everything as-is. 
In your other thread, I think someone recommended a 2037. They are good engines, they smoke, and many were originally sold with whistling tenders.

As far as purchasing individual pieces versus buying a set: in my area, there are plenty of hobbyist train show vendors who would be willing to put together a used 2037 train set in your price range. It would not be something that came together from the factory.

I am not familiar with the train market in your area.

I bought a box of used 027 & O gauge stuff at a local flee market, while most was close to junk I did get a really nice transformer in the box. It is a Troller brand transformer with 2 train capability and 2 switches for low or high voltage output; 0 to 9 volts and 0 to 18 volts. I can run my Williams without any changes to the wiring. 

Lee Fritz