Some Dr. Seuss titles have had their value take off online after it was announced that they would no longer be published.Dr. Seuss Enterprises, the business in charge of preserving and protecting the legendary author's legacy, announced Tuesday that it would stop selling six Dr. Seuss titles — “If I Ran the Zoo,” “And to Think That I Saw It on Mulberry Street,” “McElligot’s Pool,” “On Beyond Zebra!,” “Scrambled Eggs Super!” and “The Cat’s Quizzer.”The announcement came as progressive activists have targeted Dr. Seuss on the grounds that some of his books are racially insensitive.Dr. Seuss aficionados looking to pick up copies of the canceled books, though, might double-take at the price tag. They are going for hundreds and even thousands of dollars.In fact, one hardback copy of “And to Think That I Saw It on Mulberry Street” is going for $10,000 on Amazon. Another copy of the same book is going for $4,400 on Ebay.Paperback fans will find a similar story — the paperback copy of “The Cat’s Quizzer” is going for over $1,000 on Amazon. The hardcover on the same site is almost $2,000. On Ebay, you can find a hardcover copy for the low price of $1,500 .The reasons for the price explosion? They are the same reasons why rare sports trading cards and memorabilia skyrocket in price: supply, demand, and collectibility.Now that the books are out of print, the supply of new copies has a finite end. This means that, as copies are bought, lost or destroyed, the price will rise up as demand by collectors increases.Additionally, the rarity of the books adds more value to collectors, who may be willing to pay a premium for a discontinued product.Dr. Seuss’s stepdaughter Lark Grey Dimond-Cates said that she hopes the publishing house will eventually start reprinting the books “because his body of work is unique.”