As Allison said, I suspect there are big differences in bedding costs around the country and also based on how you buy it.
Buying in bulk is less expensive of course. Especially if you buy it 'loose' in truck loads like Allison mentioned. But...then storage could be a problem. I'm talking fine woodshavings by the way.
It would also depend on the size of the area you want to bed, and the floor within in. You would need more for a 12' x 12' stall with a concrete floor vs. that same sized stall with a dirt floor or rubber matts. It also depends on how often your horse is kept in his stall.
Here is my example: I buy shavings in big square bales from my local feed store in northwest New Jersey. I usually buy a dozen at a time and use them all in my horses stall at once. I have 2 horses, that stall is 30' by 30' and is open all the time. It also has has rubber mats on the floor.
The bales are around $4.75 (I cannot quite remember) a piece, so around $60.00.
In the summer, I buy/use them once a week because my horses spend most of the day inside to get away from the sun and the flies. But if it rains a lot, they spend more time outside. So that is just an estimate.
In the winter, they are outside most of the time. So I have to replace the bedding much less often than in the summer where I strip the stall once a week. (I do pick it out every day, cleaning the poop and the wet spots).
The point of all of that is...it really really depends on how you plan to stable your horse and how you plan to buy your shavings.