After a quick once over, it appears that the e-text version of Siddhartha by Hermann Hesse that is available on enotes is the very same version published by Prestwick House in their Touchstone Classics series. This makes sense as the lesson plans that are available on enotes are the ones published by Prestwick House.
The Touchstone text was translated and edited by M.A. Roberts and later revised and edited again in 2007 due to a great abundance of errors left by the original editor.
This current version is, in my opinion, now comparable in quality to the popular Bantam edition. If I am correct, and this is the correct text, it can be purchased from Prestwick House for about $4.00.