A Wired network will always be your safest option if security is your priority.
I assume you have firewalls in place and relevant anti spyware / Virus, etc tools on your systems too.
It is indeed the cheapest sollution.
I but my ethernet cable from
www.cableuniverse.co.uk and have always found the prices to be good and great delivery service.
You could wire up the easiest places and then for areas that are harder to link up, use the current ethernet power adapters you have.
If you say that you are using the highest security on your wireless at the moment, you change passwords regularly, it is unlikely that someone will single out your computer to hack on purpose.
Often, people find that they have accessed other people's networks accidentally.
However, if you want almost total peace of mind, go wired.
Nothing will be 100% unhackable though.