I think the blower went out on my furnace. Will it be expensive to fix?

Will it be expensive: that depends on two things: how it failed, and what you consider expensive.

There are a few separate things that can cause the blower to quit, and let's go through them one by one.

1) Power failure. The breaker may have tripped that serves your air handler (this usually incorporates the furnace as well, these being the indoor parts of your HVAC). Go check that. If the breaker switch looks like it's stuck in the middle, push it all the way to OFF, then all the way to ON. Did that get you going? If so, great! But keep a weather eye on it for a few days, if the breaker trips again you may need to call a tech as frequent trips are an indication of a deeper problem.

2) Failed fuse inside the air handler. The air handler has a little control board full of intimidating-looking electronic bits, and there's a fuse that interrupts the power to it. If you open up the front panels of the air handler and look for the control board, look for the fuse. It may be directly on the board itself, in which case look for one of those bladed type of fuses you see in cars, or it may be in the wire that sends power to the board. That's a squeeze-twist operation to open, don't be afraid of it, it's almost invariably just 24 volts. If a new fuse pops immediately, stop and call a tech.

Things get a little more involved from here. Please note there are certain risks involved too, you'll be doing things around live power, maybe fiddling with a motor that might start suddenly, etc. If you feel at all uncertain, STOP and call a tech. Techs are cheaper than the ER every single time. Don't ask how I know.

3) Bad capacitor for the motor. You can try this: while holding down the safety switch (a long button that the air handler panel holds down when the panel is closed), use a stick to give the blower wheel a spin. USE A STICK or something similar. Not your fingers. You'll want to keep your fingers.

If the motor itself is warm or you could hear it humming before you took off the panel, and it hums again when you hold down the button, you may have a bad cap. If the motor spins up when you give the wheel a push (in the correct direction), then likely your entire problem is just a bad cap. The capacitor looks a bit like a vienna sausage can, or a personal-sized Spam can, without the label on and a couple of wires coming out one end. Capacitors are cheap and easy to replace. NOTE: even a "dead" cap can have a jolt in it to give you a nasty bite. If you decide the cap is dead, TURN OFF POWER, then short across the all the capacitor's connections to drain its charge. Then you can disconnect and remove it. NOTE how wires were connected so you get them onto your new cap correctly.

4) Dead motor. This is the most expensive possibility. Depending on your system - and you didn't tell us make, model number, any of that useful info, please remember that next time - your motor could be proprietary, electronically controlled, etc. But I'm usually out the door of my parts supplier for less than $200 and the motor only takes an hour or so to pull and replace. The really costy bit of this is the tech's service charge and labor rate. If it's anything you can fix on your own, you're likely best served doing it yourself, or at least eliminating the easiest possibilities. That way the tech doesn't waste time on the simple stuff.

Good luck with it.