iTunes has the Star Trek: Original 1-10 Collection 10-Movie Bundle (Digital HD) to own for $20 downloaded.

Includes The Motion Picture, Wrath of Khan, Search for Spock, Voyage Home, Final Frontier, Undiscovered Country, Generations, First Contact, Insurrection and Nemesis, so you're sure to get at least 5 good movies.

Amazon Prime members can stream these movies for free.