You may never have heard of Korvac. You might care even less about who he is and what role he fills in the Marvel Universe. The important thing is that speculation about Korvac's importance is increasing, and along with that, prices are rising.
Added to that is the complication that this is a genuinely scarce book in high grade. Marvel 'square bound' books (annuals and specials) are hard to find above 9.0 generally.
The Defenders were not the most popular series, so it stands to reason that finding a copy of Giant-Size Defenders #3 is not going to be as easy as laying your hands on a Giant-Size X-Men #1, for example.
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