I don't know of a good comfortable A/P but I have an extremely comfortable dressage saddle, a Wintec Isabell. Definitely one of the most comfortable saddles I've ever ridden in...and since it's synthetic it could easily stand up to mud, water, and dirt from the trail. Every now and then you can find one used for a great deal..I found mine for $400 in pretty nice condition, only some minor wear.
And I think it's worth noting, if you're at all interested in a western saddle, the absolute most comfortable saddle this butt has ever met (and it's met plenty of fancy expensive trail saddles) is an Abetta Brushpopper, only $406-453 (depending on seat size) at Abetta Brushpopper Trail Saddle
. This saddle is INCREDIBLE. It's basically an Abetta Pathfinder but with a cloud for a seat. It has a HUGE layer of memory foam over the entire seat and it feels like heaven. Once you sit in this saddle, you will honestly never want to leave, hahaha
It also has nice padded trail stirrups for even more comfort.
And since it's cordura it's very lightweight and safe to get it wet.
I adore it.
They also make a really similar saddle in an endurance style without a horn. http://www.buytack.com/products/saddles/act/20554.htm