This is how i keep my private keys safe since i can't afford to buy a hardware wallet.
1. A complete new harddisk
I bought a new harddisk and install window 7 on it and copy all my private keys in there, i don't bother to leave this harddisk in the pc, after the copy is completed i remove the harddisk and keep it.
2.My Recording book
I have a long hard shelled book that i use for keeping records of all the airdrops and bounties i promoted because sometimes i used to forget easily so i write down my recovery seeds in this book as well
3. Flash Drive
I have a good 8gig flash drive as well that i use to copy software and files from one pc to another so i format this flash drive and copy my private keys and recovery seeds in it.
At first no one knew i am into crypto stuffs and secondly i don't share my room with anyone cos i am living alone, those who have people around them with face problems like friends going behind your back checking through your stuffs or even stealing your things, hardware wallet is still the best though.
Yes, it is manual and costly or labor intensive. Why don't you think about buying an old laptop to do transactions and just focus on working? That's the only way hackers can't hacked your wallet.
I am using my own computer to work and never use it to access any unfamiliar websites or use any technology that requests server information.
I think that's the best way to secure and save a lot of money.