EDIT: The title says SPD-SL, but really I'm open to any kind of clipless solution.

Right now I've got toe clips on my road bike (Novara Express; bought it with my REI 20% discount + my dividend), but I'm thinking of upgrading to clipless pedals for my daily work commute (12 miles one way, relatively hilly). However, while it's not too much of a problem to change into more normal shoes at work, where I can just keep a couple of normal work shoes to wear, on the weekends I like to take my bike places where I don't really want to wear bike shoes and obviously can't keep a spare pair of normal shoes.

Does anyone make toe clip adapters (or platform adapters that can accept toe clips/straps) so that I can wear normal shoes when I want to without losing the efficiency benefit?

Alternatively, are there affordable (~$100) SPD or SPD-SL shoes that can be packed into a reeeaaally tiny space? I'm talking flipflop-like compactness. That would somewhat alleviate the inconvenience of having to pack extra shoes whenever I go cycling.

Thanks for the help!

P.S.
I've already run a dozen Google searches. Most of the links I find are completely out of date (i.e. from 2009 or earlier) or have terrible reviews.