Waste of money.
1) For a desktop PC all you have to do is pop the top and add in a USB card.
2) They are still plastic, with time and effort you can pull one out.
3) For the determined person it's get laptop, take off cover, un-solder the port (only 4 wires on USB 2) and solder in a new one. But at that point you might as well just pull the drive out
Most if not all PCs can disable the USB ports in BIOS and you can also set a BIOS password so that cannot be changed without the password.
-Dave
well said, an experienced engineer will just loose the computer system, remove the hard drive, use original operating system if its windows10 and attempt repairing the OS, then using command prompt to bypass the password and gain access to the information on the hard drive and the rest is history. Even if you used an application to protect your wallet, it will just be uninstalled, and the rest is history. your computer and the airgap will be there for you unharmed, but your coins are gone.
In conclusion, this approach suggested by OP is just a total waste of money.
Most if not all PCs can disable the USB ports in BIOS and you can also set a BIOS password so that cannot be changed without the password.
BIOS settings can be reset by removing the CMOS battery, then plugging the PC. A better way is even replacing the BIOS chip with a spare from a similar Board. it only takes few minutes to execute. you just pray and believe you're not a target cos there are many ways to breach the assumed security.