How much money can you get out of a fossilized spinosaurus tooth that is 98 million years old?

The price one could get for selling a fossil of any kind depends on the type, who the buyer is, and the condition of the fossil. The tooth of a dinosaur like Spinosaurus could probably be sold for thousands or tens of thousands of dollars.

However, there are many laws regarding the possession, import, export, and sale of fossils, and they vary depending on the country and/or state or province you are located in. These laws are there to protect fossils, which are easily damaged. A damaged fossil means that priceless paleontological information is lost forever.

If you are in the possession of a fossil, especially one as valuable as a Spinosaur tooth, you need to immediately determine the laws in your area and I would recommend donating it to a local museum as soon as possible. If a fossil isn't in the right conditions and has been excavated, it is only a matter of time before pyrite crystals inside of it cause the fossil to self destruct.