Is this a simple part to replace?
Ummm, no, not really. There are actually four tone wheels on your Santa Fe equiped with antilock brakes and traction control, one for each wheel. The service site does not provide a very good description, exploded schematic or specific repair procedures to the tone wheels (at least that I could find). I assume your problem is related to the front tone wheels. I did find a schematic that indicates the rear tone wheels are part of the rear hub casting, and as such, I would guess are far less exposed and less likely to be cracked.
This graphic is from the Hyundai service site at http://www.hmaservice.com/
. It shows the front wheel drive shaft/CV joint/knuckle/hub assembly. The arrow points at the wheel speed sensor. What looks like a "gear" directly under the sensor should be the 47-tooth tone wheel. It appears to be mounted on the drive shaft between the CV joint and the wheel bearing on the inside of the steering knuckle. To replace this part, it appears you need to disassemble the brake, remove the hub, disconnect the tie rod end and partially disassemble the upper suspension so that the the knuckle and the lower suspension can be swung down to expose the terminal end of the driveshaft. Usually this is more involved that most DIY are willing to tackle. There more generalized instructions for this procedure under the "drive shaft and axle" section of the Santa Fe on the service site.
I suggest you investigate this a little further before you replace the tone wheel. I would jack the front end of the car up and secure it on blocks or jack stands (don't trust a jack as you'll be under the car), remove the front wheels and then try to visually inspect the tone wheels while turning the hubs. You may need to unbolt and swing the sensor out of the way. First of all, you still need to determine which side may be cracked. Second, it could be the teeth on one or both of the tone wheels are plugged up with mud or other debris. Cleaning the tone wheels and the sensors may solve your problem. If you confirm that a tone wheel is cracked, I suggest you have a mechanic perform the work.