If you extra PC you can make a watch-only wallet where you can make an unsigned transaction.
Just copy the public key/address of the imported wallet from your offline Electrum wallet and then paste/import the public key/address to your Electrum on Extra PC that connected to the internet.
Then make an unsigned transaction on Electrum online from your extra PC image below for reference.
After that look for export and you can use the copy or export to file.
Once you have them a file or the copy of the raw transaction transfer it to your offline PC and import it to the Electrum sign the transaction. Follow the image below
Now sign the transaction and export it again and transfer it back to online PC and import it to Electrum and then broadcast the transaction.
Oppsss. ranochigo is faster than mine. Anyway, if you can't follow his guide then you can follow mine and the images above are easy to follow.