The least expensive times of those you mentioned will be early December or January (not over Xmas / New Years). Rates do vary significantly by how busy the season is.
We just got back last week and I can tell you the week after Thanksgiving was AWESOME! Disney at Xmastime is a very special place to visit! Also, the crowds were the least I've ever seen at WDW, so we walked onto just about everything there, didn't even need Fastpasses really, the period between Thanksgiving and Xmas is now my #1 pick of times to visit! Also, the weather was absolutely perfect, hot enough for shorts but not too hot, and not so cold that we were freezing at night either (ok my DW was but the guys never were! LOL)