I always get the "yi" of 容易(róngyě easy) and 便宜(piányi cheap) mixed up... thought I would share what I found on my research of these two commonly neglected suffix characters of two common adjectives. (and aren't they the same meaning when saying someone is easy and cheap? Ha ha... okay, in Chinese can't use them that way)
易:
What we need to remember is that 容易的易 is an exact pictograph of a chameleon -- the lizard that EASILY changes color, which in fact is also a radical of meaning and phonetic in the world for lizard, 蜥蜴 xīyě.
宜:
便宜的宜 first of all has a roof, 宀(mián) and right there we can remember it has to do with shops, which is where we hope to find 便宜的东西！The 且(qiě) below the roof means "for the time being", so we can think about a sale, or something being cheap, is only for the time being, temporary 暂时(zŕnshí). 宜 it self means "suitable" as well, so something that is convenient(便biŕn the other, more commmon pronunciation of 便) and suitable is 便宜cheap(piányi)!!