No matter what base engine you start out with, you're going to either spend the money to do it right or cheap it out and build a "low-life" engine. It's your choice.
If you add up the costs for the correct parts (cams, pistons, rings, studs, bearings, gasket set, carbs/manifold/linkage, etc.), machining (case, heads, rods, crank, rocker arms, etc.) and your labor, you'll have at least $3000 into it. The cheapest route is to build it to factory specs with CIS, that way you may not have to change out the pistons or buy carbs.
The 2.7 engine is as worthy to rebuild as the others, especially if you have one already, and like other engines it gets more expensive to add power.
Sherwood Lee (w/2.7)
http://members.rennlist.org/911pcars