This is the way to provide open access - as long as they let you buy back previously published articles as well.
The journal Physiological Genomics has adopted the Prosser method of offering open access. Quoting its web site: "Starting July 1, 2003, authors can choose to pay a $1500 fee to have their article published online with Open Access from the first date of publication or choose to pay no author fees and leave their article under Subscription Access. Open Access means that those online articles are completely free to any person or any library. All online content associated with the article (text, figures, supplemental material) is freely accessible." [Open Access News]