Agree with all of the sentiments above. As I've collected these over the years, my focus has shifted away from perceived dollar value (though I still like that too)...and towards those that I find "valuable" due to their artwork and/or uniqueness. Some of my favorite pennants didn't cost me more than $50 and in some cases, quite a bit less.
Here are a couple that recently came cheap but are pretty unusual...The Raiders one particularly...in the "1967 Single Bar" style right down to the material it's made of. The Raiders didn't move to L.A. until 1982.