Personaly of the three,, I would go with a Yamaha (U1,U3,U5). Yamaha upright pianos have a stong dependability, with good keytouch response, and a great value-per-dollar. I personaly really like Yamaha's light responsive keys over Boston's and Kawai's.
As far as the repair/tune goes,, I'd say it's faily easy. Asian piano parts are not very hard to find (unless its grey market) -- cost of parts/repair relatively cheap compared to German pianos.
As price goes,, I believe Yamaha's are the most expensive of the three (the U series are real expensive).. then comes Kawai,, last Boston.. But it all depends on the size: 44, 45, 46,48,50, 52 --- and the finish.. I've seen the Boston 118S (46") around 3 grand(give or take a litte). Hope this helps.
-as