Pay-as-you-go exercise classes in Boston or south of Boston?

Hi all,

I am interested in finding fun exercise/dance classes.  I'd rather pay per class than be tied down by a weekly commitment.  I live in Brockton, MA and work in Boston near North Station so I'm looking for anything on the South Shore or near the North Station area.

Sometimes I take ballet or zumba classes at Life in Synergy near Prudential.  I like it there and would recommend it, but it is kind of a hike, so I'm looking for alternate suggestions.

Thanks!