Sometimes you can get deals on TLs, but not often. I usually see them for $400-900 depending on condition. $700+ is used Tremec territory.
Like Thumper said, original bigshaft Toploaders are uncommon and highly desirable(read:EXPENSIVE). David Kee Toploaders has every part imaginable for them, even brand new assembled transmissions. You also need to be aware of the first gear ratio like Thumper also said. A 2.32 first is a close ratio trans. It has a tall first and 2-3-4 are close together. A more common 2.78 first is a wide ratio trans which is easier to drive on the street with sub-3.89 rear gears. A 429/460 probably wouldn't have trouble with the 2.32 first, though.
Like Thumper said, original bigshaft Toploaders are uncommon and highly desirable(read:EXPENSIVE). David Kee Toploaders has every part imaginable for them, even brand new assembled transmissions. You also need to be aware of the first gear ratio like Thumper also said. A 2.32 first is a close ratio trans. It has a tall first and 2-3-4 are close together. A more common 2.78 first is a wide ratio trans which is easier to drive on the street with sub-3.89 rear gears. A 429/460 probably wouldn't have trouble with the 2.32 first, though.