In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Forget about the Dole vents. You should go with Gorton vents. You can look at their website or call Ken Kunz at Gorton at (908) 276-1323.
In the meantime, check the length of your mains and the diameter of the mains as well. Send back the dimensions. If you do and Steamhead replies, listen to him. Properly venting the mains can save you a lot of money and I think Gorton has the best product.