I think you will find that O gauge Hi-Rail is a lot more of plain fun, and a lot more forgiving in operation, than HO. At least, that has been my experience.
Another way to see what is out there, is to go to the "Bay" website, and go to Model Trains, O-Gauge, and select locomotives, cars, accessories etc. You can even select these items by manufacturer.
If you browse through the listings once a day, you will new and used products dating from 1920 or so, to last week. Most engines and rolling stock items have several close up pictures, plus good descriptions. Pretty soon, you are going to start seeing things that "catch your eye", and you'll be saying "Wow, I really want to get one of those." And, you can write it down.
The prices listed are almost always too high, but they definitely give you a context for the price, especially if there are two or three sale listings with different prices for the same item in different conditions. If you go to a small show and find the item for 10% to 15% less, then I think you got a good deal. Is the lowest possible price? No, but your goal is not to search for years for the lowest price, but to get what you want.
And, if you check the For Sale topic on this Board every day, you can also find good sales.
Also, if you really want a used item, at a fair price, you can always put it in the Wanted section of this board. I have done this three times, and other Members with extensive collections have sold the items to me a very very fair prices.
I had to laugh when I read about guys at train shows with 3" thick notebooks containing there wish list. My wish list is generally 3 items written on a single piece of paper.
On the other hand, if you are interested in getting into the O-Gauge hobby as a serious collector, and wanting to collect rare sets or items, then I think you are on a totally different "track" than what I have described above. And, you will be destined to the joy of attending lots of shows, occasionally finding these things, and having to do some serious negotiations and laying out some serious cash (the same as with HO).
Hope this helps.