Orbi RBK50 daisy chain or line of sight

I agree with FURRYe38 that connecting to a WiFi access point that is 125' away is unlikely to be satisfactory.  If all you want to do is check email, perhaps.  Stream video? No chance.

I agree that burying 125' of outdoor, 'burial' ethernet cable is a "job".  There are people who will gladly bore under the driveway.  Check out this fun video: https://www.borit.com/blogs/news/51099331-save-money-digging-under-sidewalks-and-driveways 

Ironically, the cost of the direct burial Cat6 ethernet cable is minor compared to the cost of penetrating two buildings, trenching 125' (and under the driveway), laying conduit (if something happens to the cable, you do NOT want to trench again!), installing the cable, terminating, etc.

The only reason to purchase the expensive RBS50Y is if you want to penetrate the house wall and mount it "outside".  The signal still has to carry 125' and penetrate the barn wall.

I am more a fan of a WiFi point to point bridge.  Netgear makes one, as FURRYe38 referenced.  There are less expensive options, depending on what total throughput you want.  If your needs are modest, Ubiquiti's "Nano Station" products cost under $100/pair and can be mounted inside.  (Check out the cute "window mount" where you stick it on the inside of the window.)  If their ratios will carry 5km or 15km, they will certainly penetrate a barn wall. A package of two LocoAC units that provides 450mb performance is about $150.

I have no personal experience with Ubiquity.  Almost every networking manufacturer sells "point to point bridge" products (including Netgear).

You might spend a few minutes reading the "Amazon reviews" of some WiFi bridge products.