Re: Looking for an affordable, dark sounding acoustic.
Are you looking for a straight up acoustic, or is an acoustic/electric a consideration?
With an acoustic/electric, you'll have an EQ to help darken the tone.
Concerning Seagull--those are fabulous! Sound and play great.
Another consideration is Blueridge. They are basically pre-war Martins without the price tag. They used to be dirt cheap, but have gone up considerably. You may find an inexpensive used one.
Oh, and Treva--what the hell are you doing in here? You've got company (o)Y(o)....lol.