Fossilized teeth or modern? Ebay will net you more teeth than you can handle. Not bad of a collection to begin though honestly, can be fun and rewarding. To save you money in the long run...systematic collection is best.
First: species
2nd; Location
3rd: era
4th: size
5:condition
Just a suggestion.
And I was fortunate to find 3 megalodon teeth in the Santee Cooper basin in S. Carolina 8 yrs ago in an area now off limits to collectors.