How can I tap an unused well for outdoor watering?
If you are fundamentally opposed to (or trying to avoid paying taxes on) an aboveground structure, you could bury a vault to put at least a small pressure tank in. With use of a "constant pressure valve" or a variable-speed "constant pressure pump" you can get away with quite a small pressure tank (2-5 gallons) but you really can't run a pump without any pressure tank, at least not remotely efficiently (you could, I suppose, put a pressure-relief valve in the line at the top of the well, and run without a pressure tank - the excess pressure would recycle water down the well, but that's a terrible waste of power...)

If you really need water in the winter, bury the whole thing below frost line - one common method is to use 4 or 6 foot diameter concrete well tile (as used for shallow dug wells) placed over/around the drilled well casing to provide the frost-free vault - you can insulate the top and sides for better effectiveness. While you have a backhoe in to dig for that and the power line, dig some trenches below frost line to where you want to have hose spigots, and put "frost-free hydrants" at each one (they have a valve at the bottom, and leak away the water in the upright pipe between uses.) Might as well have the backhoe dig 100 holes for trees while you have it, too.

If not fundamentally opposed to a structure, an aboveground structure (small toolshed for the orchard) above the wellhead might be a less expensive approach, unless the local taxing authority makes it an expensive approach after all (that can happen, and is best to be aware of when deciding.)  The area with the pressure tank can be heavily insulated and electrically heated to 45F or so if you really need water to hoses in freezing weather, or you can drain the whole system in the fall and start it up again in the spring if you don't really need to use water from hoses in the winter.