There is no way to cheaply build a 426 or any hemi for that matter. Any used 426 parts must be looked at with a very cautious eye. Most have been damaged from racing and are junk.
In '64 when Chrysler first started building the Hemi for NASCAR racing they started with the 426 wedge block. It quickly became apparent that the bottom end of that block wasn't strong enough. They redesigned the bottom end which resulted in a new hemi only block. I am most familiar with the early hemis so I'm not entirely sure but I don't believe you could successfully use a 440 block with the 426 heads. You might be able to use one of the 426 wedge blocks if you could find one but they are pretty rare and it probably wouldn't hold up to any abuse.
Your best bet if you want a reliable hemi would be to bite the bullet and go down to your local Dodge dealer and buy a 426 crate motor. They aren't as expensive as the "enlarged" versions and shouldn't go much more than about $9000. If you add up the cost of buying the parts new separately it’s a very good deal.
If your budget won’t allow that then I'd pick up a used 440. They're dirt-cheap and will make a whole lot of power for half the cost of the 426.
Good luck
Centerlne
http://www.hotrodsandhemis.com