Backing up to a second USB hard drive would be the cheapest and easiest way to go. I would not recommend cloud. The yearly fee for one year would pay for your new hard drive.
I have all of the USB ports on my laptop in use;
This is what USB hubs are for. You can buy one for a few dollars. You will get the best speed results copying files if the two hard drives are ultimately connected to different ports on the laptop, instead of both being connected to the same USB hub.
Also, not sure what USB version I have, laptop is around 9 years old.
You will need to find out. Google "how do I tell what usb version I have". The inside of USB 3 ports is usually blue, but not always. USB-C is a different shape connector, but your laptop is too old to have USB-C.
Also, what program can automate the syncing or mirroring of two drives as I won't remember to do a nightly, or even likely a weekly syncing.
This is not a technical problem, it is a you problem.
You might consider investing in a calendar and make a notation on a specific date. Windows has a built in task scheduler you could use along with a batch file, and if you google for any backup software, they usually have built in scheduling capability. But there's a problem with assuming your memory can be replaced with software, considering the position you're in. You're backing up a laptop (a portable device) to portable external hard drives. Using scheduling software is problematic when in that situation, because the computer must be ON and both hard drives connected and on when the scheduled time arrives. If you can't remember to plug the external drive in, then using the scheduling software to supplant your memory to actually run the backup will not achieve success.
Remember, once you have made your first backup, it's not life and death. With no backup at all, you can lose your entire collection. Once you have made a single backup, you're no longer at risk of losing the entire collection, it's just a question of losing the changes you made since your last backup.
Purchasing new music is a manual act. Perhaps you should just backup your collection after you have added new music to it. Then you would only lose tag changes if you have to revert to a backup. You can adjust your backup frequency based on how many days/weeks/months of tag changes you are willing to lose. If you only purchase music infrequently, you would not need to backup very often at all.
If you're the sort that is changing your music collection all the time, and demand that you never lose more than a day's worth of changes, then you're simply going to have to be more diligent about backing up, or spend a lot more money to invest in an automated NAS-based backup system, and even then you would still have to remember to take your laptop out of your bag and connect it to the network every night, assuming your laptop travels around.
Good luck...