Two of the leading makers of electronic-book readers, threatened by the success of Apple Inc.'s iPad, slashed prices Monday in a move that could further drive e-readers into the mainstream.

Early Monday, Barnes & Noble Inc. cut the price of its Nook e-reader to $199 and introduced a Wi-Fi-only model for $149. Hours later, Amazon.com Inc. lowered the price of its Kindle e-reader to $189.

Both...