If you don't want to buy a hardware wallet, you can use Truecrypt or Veracrypt, both free encryption programs, but they are not for newbies, with these programs you must know what are you doing otherwise you risk to accidentally delete a portion of your HDD where you may well have stored your wallet.dat files. Read thorough descriptions and faqs about them and youtube videos also and if you feel confident you can go with them. They are very powerful encryption programs and it is very difficult for any hacker even if they access to your computer to hack them.
What Truecrypt or Veracrypt does it makes "disappears" a portion of your hardisk, and only you with the key (password) of the program can restore it back. Do so with your wallet.dat directory whenever you do not need to use it.
The problem with a lot of desktop wallet programs is that they don't allow you to choose where you want to install your wallet, meaning which drive or folder. They usually just install it into C:/
If using Veracrypt you would need to create a container which will be encrypted. But if the wallet program doesn't allow you to choose the location of where it will be installed, then you wouldn't be able to install the whole wallet program into that container then dismount it so that container becomes encrypted.
Maybe another option would be to install the wallet programs normally into C:/ then use GPG4Win to encrypt the whole wallet folder. Thoughts?