US Deluxe is $99 a year, or $19.95 a month.
World is $199 a year, or $29.95 a month.
Pretty good prices considering you sit at home at 3 in the morning and research (what you wear is at your discretion--libraries and archives are less flexible about clothing).
Ancestry's site has more information on the price reductions.
Just remember, to keep track of what you sign up for. The only thing to keep in mind is what it costs to actually visit libraries--for those of us who do genealogy "after work" being able to use ancestry.com whenever we have time is a significant advantage (no driving, parking, etc.).
As a note, I only mention on this site databases, software, or books I have actually paid for myself and use myself. If there's something you do not see here, it means that either I haven't found it useful for me or it covers a geographic area in which I have no interest. One can't buy every program or book that comes along and I don't like to suggest things to people if I haven't purchased them and used them myself.