Quoted:
I guess I could try INSTEON...but I would need an INSTEON hub.
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You DO NOT have to have an Insteon hub at all. You can link two switches or a switch and remote together without a hub.
A hub is required only if you want to add programmatic control of your system. Timers, iPhone control, web control, time of day based reactions, etc. A hub is not required to simply have a remote switch in the house that operates a circuit in your shed.
I have Insteon stuff all over my house an love it. You can get it at Smarthome.com like another user posted.
ETA - Discuss the wireless range with Smarthome if you decide to get a wireless remote to make sure it will reach. If it was me, I would probably install a wired Insteon switch in the house to avoid poor wireless communication and having to deal with batteries. Since Insteon communicates via the common wire as well as wirelessly, it can communicate across circuits in your home. No need to run a wire from the switch in the house to the shed.