You don't need to spend more than $50 to find a fully functioning typewriter in good condition. The only time I could see spending an extreme amount of money for a restored machine is if it was of significant historical value, or if you were investing the money in refurbishing a family heirloom. It's also worth noting that most of these restored examples that you see online are not professionally restored at all. For example, I know of someone in my area who buys typewriters for around $50, cleans them up, oils a few parts, and then flips them for the prices you mentioned. He's just a middleman who profits by misrepresenting who he is and what services he performs.

As for the two excellent models that you're interested in, there are very common and with a little hunting you should be able to buy either for next to nothing. And if you learn to clean and perform a little maintenance yourself you'll save a lot of money and be far more familiar with your typewriter.

Those are good, solid choices. You should be able to find a good one of each. Just compare appearances. If it looks clean and without rust, you have a good chance at getting a good one. Make sure it has a good case, too. You should be able to get a good SC Silent, perhaps needing a little cleaning and a new ribbon, for no more than $100. The Olympia might be a little more, say $150 online. I found my 1946 Silent and 1958 Olympia at antique stores for a lot less.