A Fantastic or Maxx fan on high could do a complete change of air in a small TT within just a few minutes. Even on low or medium, it will draw a very nice breeze in through your windows. So whether that would be enough for you depends on the temp and humidity levels outside, and your personal comfort level.
Personally, just sitting around in the TT on a reasonably dry day I am ok up to about 85 degrees during the day, but I like it to be below 75 when I try to fall asleep. But if I were in the Pacific NorthWet, I might feel differently! I hear tales about your humidity levels. I don't like feeling sticky or being under sheets that feel damp, and A/C dries the air so much.
If you're trying to economize, install a 3 speed fan along with a MaxxAir vent cover so you can leave it open 24/7, even in rain. I think this item is well worth having for comfort's sake even if one has an A/C as well, because 90% of the time I can be comfortable with just the fan-induced breeze (and I tire of the A/C noise).
But if you decide to get an A/C, have you considered something like an 8000 BTU window unit? Much cheaper than a rooftop unit. Some folks install them permanently through either a window or a hole cut in a wall.