Mahogany is commonnly used for porch material in your area.

Aside from that, I'm not too sure about how it compares in cost to Ipe.

When I've visited New England I was surprised to see so much Mahogany used for porches, even in new construction. I believe it holds up extremely well in that climate.

Out here in CA, I've seen some older park benches made of Mahogany. It holds up in this climate about as well as Old Growth Redwood. That is 30+ years.

Mahogany is a good decking material, but very expensive.
Be careful though, as some suppliers sell Lauan as Mahogany.
Lauan is also called Phillipine Mahogany, but it's not good for external use, and it isn't Mahogany.

steve

We're by boston and have Mahogany. As long as you have good ventilation under the deck your good to go. Also, make sure you use a stain that is designed for hard wood like cabots. Behr, Thompson, Olympic stains won't soak in. I made that mistake. TPW looks great on it.