I was going to suggest something like that myself. When we bought this place I got a pair of walkie talkies for ~$20 at HD for this purpose. They do the job.I have a pair of Kenwood handi-talkies. KPG-87D. Rechargeable LI batteries and, supposedly, five mile range. Operate under the FCC - MURS program. One kept at home - the other with me - anywhere on my property. No muss - no fuss. 100% operation - 100% of the time.
Good points. Another option would be to run fiber. No grounding issues, and you can make a lot longer runs, though it is a bit fragile. Unless you have other wiring to pull, the point-to-point IP link would probably be the easiest option.Since the house and the shop are on different power supplies, and given the distance, and the location (weather), if it were me, I would not pull a conductor. Wireless point to point WiFi, or cellular amplifier would be my choices.
Ethernet (cat5) is good for a maximum distance of 100m/330' with good cable. Cat6 is only good for 55m/180', and Cat 6A is good for up to 100m/330'. To me the issue is going to be lightning storms and the induced voltage on long ethernet runs outside, and the different power supply and grounds in the two buildings is likely to make it worse.