Depending on your ottoman furniture, how much it will cost to reupholster the ottoman will vary.
Also the condition of the ottoman piece will also affect how much it will cost. If it's in relatively good condition, you can just change the fabric and put everything else together. Otherwise, you might have to change the frame, legs, and basically start from scratch.
Recommended:
Is Reupholstering an ottoman worth it?
If you enjoy fixing things things, and are not afraid to get dirty, it can be a relaxing way to spend your weekends. Fixing things should feel more of a hobby, because fixing broken furniture in most cases will save you some money, but considering the amount of time you spend getting the materials and fixing the furniture, you might actually be losing money when we considering all things.
If the ottoman is in good condition
If your ottoman is relatively in good condition, then you should be able to reuse the wooden legs, the main board, and underlining hardware.
You can choose to replace the memory foam and padding since they are relatively cheap to buy a new one, but you don't necessarily have to.
If everything is in good reusable condition, your costs might just be a few nails and tacks. You can wash the fabric and attach it again, or if you prefer you can buy new fabric to attach to your ottoman which will cost you.
The material and the surface area will affect the price. But for a small ottoman bench, it could only cost you 10-20$ worth of fabric.
If the ottoman is in poor condition
If the ottoman however is in bad condition, you more than likely end up losing more money trying to fix one piece of ottoman furniture. The foam, cotton padding, underlining board, fabric etc can cost up to $100 or more depending on the size of the furniture.
You are also spending your time buying the materials and fixing them. So unless the furniture piece has sentimental value or is quite expensive, it might not be worth the time to fixing it.