Backlight had been flickering and now goes off after a few minutes

For about the past month, the backlight on my laptop has been flickering and now it just completely shuts off a few minutes after I turn the computer on. I knew this was coming eventually, as every time it would flicker, I would hear something like an electrical sound coming from the screen as it flickered. When I shine a light at the screen, I can still see everything fine, so it's not the screen itself, just the light. It's a Toshiba x500-q900s and well past it's warranty. It would cost well over $400 to send it in, and I don't really want to pay that.

When I shine a light at the screen, I can still see everything fine, so it's not the screen itself, just the light

The flashlight trick revealing the Desktop does indeed indicate the computer itself is fine. But it does not necessarily mean it is the light (CCFL - cold cathode fluorescent lamp). Typically, it is the inverter that fails, though they are often both replaced together, which I think is wise.

This is something many technically oriented users do themselves, though it can be tricky. I generally recommend having a technician do it because they have the right tools and experience, and because they are responsible for any collateral damage.

$400 is way too high. Don't bother to send it in to Toshiba. Rather, call around to local shops. Replacing inverters and CCFLs is something most shops do daily. Parts are typically $50 to $150 depending on the screen, and labor should be no more than 2 hours, typically just 1.

Many shops charge a flat rate because they do it so often. And there are even several repair sites like Ztronics Notebook/LCD Inverter Repair.

In the meantime (or even as a permanent alternative), you could connect an external monitor or TV (and external keyboard and mouse) to your notebook and turn it into a desktop.