I believe that by comparison to the Etudes, the Preludes are much less difficult (correct me if I'm wrong). That's just my opinion.
From a technical viewpoint, to learn the Preludes in there entirety would be easier than learning all of Op.10 or Op.20, however, don't be fooled by these Preludes as some of them require just as much technique and ability as some of the etudes, and from an interpretive/musical viewpoint are also difficult.
I think the 'easier ones' are No.4 in E minor, No.6 in B minor, No.7 in A major and No.20 in C minor, all of these are technically easier than the rest but still hold many pianistic difficulties, such as voicing, clever use of the damper pedal, and in No.20's case - large chords spanning over an octave.
By the sounds of some of your previous repertoire you will have no problem playing the preludes including some of the more difficult ones (No.6 in F-sharp minor). My advice is to go out and buy a copy (you can get them pretty cheap, Alfred Masterworks sells a lovely edition at a great price) and have a play through a couple. Afterall, you shouldn't be too concerned with difficulty if you're passionate enough about a piece of music and want to learn it badly enough.