Best offer available right now is $50 for internet & phone for 6 months, afterwards bumped up to $60/month.
Standalone internet service isn't cheaper. You can try calling retention to extend your promotional rate, though recently DDFers have been unsuccessful.
The best available promo for Optimum internet (only), is the $40/month for 12 months for new customers.
Many people reported success in retaining the $40/month plan (after 12 months) after calling Optimum to cancel.
The old promo for internet was $30, but that has been replaced with the $40 plan around May 2013.
As of now, it isn't coming back, even with persistent HUCA, but users have had success upgrading to a higher speed plan for $45/month