I saw a nice example of an eggcorn the other day, advertising a "pre-fixed" menu. This is of course referring to the phenomenon of a "prix fixe" menu, where restaurants offer a multi-course meal for a set price (typically one that's cheaper than expected). Even though I don't speak French, I've always thought this phrase was fairly transparent: as an English-speaker, I'm familiar with the fact that French adjectives (like most other Romance languages) have adjectives after the noun -- we even have some traces of it in English, e.g., Attorney-General. And if you know that much, it's not a big stretch from prix fixe --> price fixed --> fixed price. But for someone who's only ever heard the phrase pronounced, the similarity might not be as obvious: /ˌpriːˈfɪks/. This certainly does sound almost identical to a standard pronunciation of "pre-fixed". And since prix fixe menus have a price that's already set, the semantic notion of a menu being "pre-fixed" makes sense as well. Phonetic similarity + semantic compositionality = the perfect scenario for eggcorn formation.
Just for fun, some examples that I found online:
Jerome Stueart interview (pt. 3)
5 weeks ago