Thanks Quamera...I couldn't think of the term "dock": precisely what I have in mind with relay/charging stations.
i'm part owner of a [disused] farm...approx. 42-44 acres mixed arable/dairy/small holding [no sheep]. The dairy herd used to make its own way to the milk shed come milking time, apparently, in my grandfather's day.[there is now a motorway dividing the farm (no cows) causing problems]
much depends on economies of scale and usage reasons. For example, Darpa I think, is trying out a pocket, tethered minidrone for soldiers [sees round corners, scopes out risks]

erfectly sensible. However, consider your several hundred acre ranch....entirely different matter; plus...do you use the drone for locating your herd in open grazing? dropping off feed/ triggering trough filling? actual herding up manoeuvres? search-and-rescue [stray sheep, lost hiker?] ??
http://www.dailymail.co.uk/sciencetech/article-1380410/A-cell-tower-suitcase-Phone-company-sells-portable-wireless-disaster-zone-emergencies.html for dedicated SAR at $15,000-$45,000 is one option for fully mobile temporary cellphone tower [plus satellite phones]... but beyond most budgets of most RT/drone enthusiasts.
I buy most my drones from China - secondary control unit motherboards, receiver boards, transmitter boards /other parts are relatively cheap .[ I like to have spares for emergencies, manufacturers ditch drone lines regularly after a run of a couple of years]. Models typically use between 3.7 to approx 12 volts power... rechargeable batteries/ rechargers are easy to come by, but solar-cell units may be costly [e.g.
Solar Power Charger Best Deals + Online Shopping | GearBest.com ] and, a gizmo to regulate/normalise the charge [create a steady rate and quality] is advantageous.
By far the greatest strain on any flying vehicle is the weight of its batteries....hence docking systems are ideal, as auto-mechanical swap-out of battery cartridges increases error/failure, is cumbersome and engineering intensive.
as you can see, with transmitter/receiver boards and control boards costing £10-20 or less cost is not necessarily capital intensive. ranches using electrical fencing tend to wire at 12-24volts [1-2 car batteries equivalent]
existing software can map docks/relays as GPS waypoints; however to get a drone to evaluate it is quicker/safer to reroute to an alternate base/charging station will require serious programming. in the case of mobile stations, how exactly a drone might orientate to it and return...any bright ideas anyone?
portable MYFI units are useful, but have limited range, and do not work in signal shadow/poor mobile phone signal coverage. e.g. under cliffs, in valleys, behind hills, or signal black-spots.
happy, and safe flying folks!
#furtherfood4thought