Some keys on Macbook Pro suddenly stopped working

I have a mid 2012 Macbook Pro 15" Retina display.

Today I was doing some work on it (sending some emails and writing a word document) and all of a sudden out of nowhere some of the keys just completely stopped working. They had been working totally fine for the hours I had been doing my work leading up to this, it just happened out of nowhere.

The keys that have stopped working are the following five: F12, ~, =, {, }

I have read the Apple troubleshooting page on what to do if keys are not working, but this has not helped. I have also reset my SMC, and reset the NVRAM.

When I connect my external usb keyboard the keys work perfectly fine on that (it's how I wrote above which keys aren't working), it's just the internal keyboard which seems to not be working... I just upgraded and did a fresh install of OS X El Capitan a few weeks ago as well, so originally I thought maybe it was a bug with that, but I haven't really had any issues with it until now and non of my troubleshooting has made it work either, so I'm starting to think it's a hardware issue.

Unfortunately I don't have AppleCare or any sort of warranty, I'm going through school and really can't afford to spend much to repair this. If anyone has any ideas of things I can try to make it work again that would be very appreciated!