Help for my hyundai

2000 Hyundai elantra, 103,000 miles, having a problem, turn knob for heat, not working- nothing blowing out of vents. Can anyone please advise on possible cause as well as estimated repair cost. Thanks

Is the blower fan running or not and is it inoperative on all speeds? That can make a difference on the diagnosis.
If the blower fan is not running on any speed then it could be a fuse problem, fan switch problem, or a faulty blower motor; probably the latter.
If the fan is running and you cannot feel any air flow then there is a problem with one of the doors in the heater/A/C box.

I cannot give you an estimate as that can vary wildly depending on where the parts are procured, the locale, shop rates, etc.
If the fan is not running then check the fuses before considering a shop repair.

The blower motor isn’t working or just that nothing activated when the heater was turned on?

Perhaps a blown fuse, blower motor relay or even a bad switch.

I am guessing it does not blow any air on any setting. Does it make any noise? Does any heat come out as you drive? Is this a fancy computer controlled system or is it manual?

The fan is not running at all. I thought it might be a fuse problem myself, but I looked in the fuse box, could not tell which fuse it might be, they are not clearly labeled as such. Any advice?

It does not blow any air at all, or make any noise. I think it is a manually controlled system.