Underground rated fiber cabling is around $1300 a mile on Amazon in 1000 ft spools, and I bet you can get a much better deal than that if you buy in quantity direct from Corning. At that point it's mostly labor and a mule is a darn clever way to save on labor costs. Also, rural folks are used to physical labor. Another advantage to laying fiber in a rural area, especially out west, is that you need to negotiate with far fewer landowners than you would in a more densely populated area, and many of them will probably let you lay the cable for free in exchange for a connection.