For what you want, modifications to the transmission and driveline and probably even suspension and brakes are required, no matter the engine so that is a wash.
Going turbo jacks up the cost quite a bit but it will also allow you to achieve the power you desire while retaining a very streetable engine. Twins are more for show for only 400-500hp and an unnecessary cost. Boost is not at all required to get 400-500hp out of a Y but you will loose some streetability (or truckability) to do it without. Naturally aspirated, once you get to about 1hp/ci, forget using it for truck things. That applies to any engine and is something to consider. It should do light duty things ok but don't plan on hauling or towing heavy loads.
For cost, get out a pencil and paper and configure a Y and a 351 and see which comes out better. For lower powered builds and considering only the cost to build the engine, the 351 absolutely will come out cheaper but as power increases and more specialized parts are required, costs start to move closer and you also have to remember the cost to actually install the 351 into the truck..
Your best source for parts will be www.ford-y-block.com.
People who have done it. Both of these are in the neighborhood of 1000hp, one for racing and one for street:https://www.facebook.com/HollowHeadsDragTeamFinland/
Possible source for your turbo, http://workturbochargers.com/index.php