They do exist, and the price difference isn't crazy. This site has plenty with the electrically actuated lock-out. (Note: a manually activated lockout is an option, but the electric one is more fool-proof as you might forget to turn the lock-out off on the manual version.)
https://www.etrailer.com/dept.aspx?furl=...=-sb-Price
Here's an electric reverse brake lock-out solenoid that can be used to retrofit an existing surge brake system:
https://www.etrailer.com/Accessories-and...11993.html
And here's a universal vehicle wiring kit with the five-flat connector:
https://www.etrailer.com/Custom-Fit-Vehi...19177.html
Both of those have videos that go into great detail on the items.
https://www.etrailer.com/dept.aspx?furl=...=-sb-Price
Here's an electric reverse brake lock-out solenoid that can be used to retrofit an existing surge brake system:
https://www.etrailer.com/Accessories-and...11993.html
And here's a universal vehicle wiring kit with the five-flat connector:
https://www.etrailer.com/Custom-Fit-Vehi...19177.html
Both of those have videos that go into great detail on the items.