I set up code signing for an electron app relatively recently. Best option I could find was Digicert. Really sucks that this stuff is necessary nowadays and not free, but it's not so bad.
That's for Windows - for Mac you'll also need an Apple developer account, afaik they're the only people who can issue certs.
EDIT: Woah, I take that back. Digicert has now gone up from $74/year to $474/year, which is crazy. I now also need a new certificate provider...
For Electron signing we use Tucows Code signing certs (you need to register as Tucows auther for free) which are provided by Comodo for $140 for 2 years.
Didn't have any issues besides getting a proper CI/CD process running.
We chose the "Open Source Code Signing" option, with it being stored on a physical keyfob thing (eg not "in the cloud"). Total cost, including the new key fob and super expensive, week+ delay, mandatory postage (!) was around 135 Euro.
For my project (quarkjs.io), I went for https://comodosslstore.com . They have the cheapest certificates I could find (at ~75USD), also they are the only ones issuing certificates for individual developers.
That's for Windows - for Mac you'll also need an Apple developer account, afaik they're the only people who can issue certs.
EDIT: Woah, I take that back. Digicert has now gone up from $74/year to $474/year, which is crazy. I now also need a new certificate provider...