Sail or Power or Motorsailer?
The other posters have made some very good points. It does not sound like you are interested in sailing, but I could be wrong. And true, sailing is a love.
Some things to consider, given what you are asking for: 40ft powerboat to cruise 1000 or more miles of bluewater, perhaps in rough weather. Generally, powerboats of that size get about 0.75nm/gal, unless you get a single diesel trawler. Single diesel trawler mpg will greatly vary from 2-6 depending on the powerplant, its age and the boat. I would use 2 and a price for diesel of $2/gal (it also varies greatly and can actually be more expensive than gas some places). I would count on every 1000miles costing you $1000.
Powerboats depreciate much faster than sailboats. Many bluewater sailboats go for what they sold for 10-20yrs ago. Powerplants in powerboats can go in 10yrs and the boat may need to be repowered. Re-powering with diesel is VERY expensive, 10''s of thousands.
Stability. A 40ft, cruising type single engine powerboat in a real blow is not someplace I personally would want to be. Many 40ft sailboats,by contrast, can be considered world cruisers and capable of handling just about any weather. A trawler going 10knts will take 100hrs to cross 1000 miles. Thats quite a bit of exposure to changing weather.
Also, depending on a single engine for all your movement in bluewater, to me, is not a good idea. If it goes, you are literally dead in the water and at the mercy of the elements and in need of rescue. Twin engine powerplants are twice the expense both up front, in maintenance, in repowering (count on $50k) and in fuel.
Most likely, if you went to a trawler web site, you might get a different opinion and true there are some VERY good world cruising trawlers (Krogan?, VERY expensive). The above is my personal bias, having cruised off shore in sailboats, crossed big oceans in only big Navy ships, and having run 32-34ft sport fishers.
Motorsailer...maybe a good compromise. I am just not very familiar with them. I do hope this helps.