I did the floors in our 110+ year old house before we moved in back in October. It was quite a bit of work, but in the end the total was maybe $600 for sander rentals, sanding belts/discs, and poly. I used the Minwax quick dry oil based because we were moving in the next week and still had to finish a bathroom.
Total was around 1500 sq ft, so at $3/sq ft that would have been $4500 or so, or about $3900 more than I spent, though it would be marginally prettier. After you put the furniture in though, it's not as noticeable.
Our first floor is very similar, 3/8" oak strips over tongue & groove subfloor. It was not original. The second floor is original heart pine, absolutely beautiful if done right.
I'd rate my job a B- mainly because the upstairs had a ton of wood filler between the pine boards that really should have been scraped out and redone. Since we didn't do that, pieces/dust would come up when I was laying the poly so our finish has a lot of 'stuff' in it, but really it matches the character of the wood and you don't notice it unless you're looking.
Pics of before/during/after for the oak downstairs and pine upstairs.