Your first typewriter? I'd strongly suggest getting the free one from your mother-in-law to start. Use the machine, become familiar with how it works (and how everything should work), and discover through practical use what you like and dislike about the machine. With that newly obtained knowledge you'll be far better equipped and have a more critical eye when looking at machines that you would actually have to pay money for.

Uwe:  You have a good point there.  I'm still trying to get a list of what machine(s) she has, but it would surely be useful to get a little experience to gain a better sense of what I like.  I should mention that while this will be my first time owning a vintage typewriter, I actually have used a typewriter before.  Our family had one when I was growing up and I took a typing class in High School back around 1986 or so.  Also, even if I don't act on it until later I'd still like time to do my research beforehand on my "short list".

mre12ax7:  I agree that this looks like one of the hotter finds.  I've had no trouble locating multiple KMM's for instance leading me to believe that I can get one later on without much trouble. 10's appear more rare and should be followed up on.

And by way of an update, the Olympia SM9 is sold now since this morning.  A reminder not to tarry too long but to seize the moment?  I'm going to call the Royal 10 seller and see what more I can find out about that particular machine.  However, I will also try not to go too overboard until after Thanksgiving.

One more update about the Underwoods...  Apparently the Leader may have been a budget model, so it may or may not be superior to the older Underwood Portable which I'm still trying to pin down and get a price for.  This is taken from http://oztypewriter.blogspot.com/2011/11/underwood-portable-typewriters-1919_22.html

"In 1949, another model was added to this line, the Leader, which was a much more basic version of the Universal-Champion."

However, the Leader I'm looking at is an earlier model so I'm not 100% sure this still applies.

OK, good to know.  So, maybe a greater chance of reliability issues then.  Also, turns out the Portable was mis-listed.  It's in Kentucky not Atlanta, so that's off the list.

Yeah, it's probably tricky to know which budget models used cost-cutting measures and which merely omitted certain mechanisms from the higher end machines.  I don't know that fewer features on a 30's model is a big deal.  If you want more gadgets you're probably better off getting machine that's a few decades newer.

So I've got an appointment to go see the Royal 10 this Saturday and I've preemptively gone ahead and ordered a new ribbon/spools for it to arrive Monday since it doesn't have one at all currently.

Speaking of tabulators...  From what I can tell, it's pretty common for a Royal 10/KHM/KMM/etc... to be missing most or all of its tab stops.  Is there anywhere that sells replacements, whether original or just reproduction "functional" ones?  I may get lucky and it's still got some, but just thinking ahead here.

Yes, the manually moved ones are what I mean.

I found this article describing how to make replacement tab stops for an LC Smith, the same method may work for the Royal as well I think if it comes to that:
http://www.instructables.com/id/Making-tab-stops-for-an-LC-Smith-Typewriter/

I don't have the metal cutting equipment mentioned in the article but perhaps a Dremel would suffice.  They're certainly not as nice as the originals but they'd likely do the job.