Learn Jazz Piano is an excellent site providing free lessons:
Want to learn some blues licks? We’ve got ’em- just go to the Blues Licks room. How to harmonize melodies? That’s here too. Jazz piano scales, jazz piano chords and jazz chord progressions, jazz piano theory- it’s here. All the tricks of the trade that professional jazz piano players use all the time, free for anyone who wants to study jazz.
Why free? There is a great jazz piano community here and it’s a privilege for me to be a part of it. Not only do I enjoy interacting in the forums, but the amount of jazz studies information here always gives me something new to work on at the piano.
The real cost jazz piano lessons and learning jazz in general is the time you spend as your life is dedicated to practicing the piano, learning the music, and adjusting to the life style of a jazz piano player.
The Simple Blues lesson is a small, useful example of what they provide:
The blues is something you should know in all twelve keys because the blues IS the cornerstone of jazz. Knowing the blues in 12 keys is such a universal jazz law that people don’t even have to mention it.
Now to find time to practice.