One of my most memorable moments was in 1993, when I heard music coming out of some cheap Mission 760i's, fed by a Rega Planar 3 & Naim Nait 2 combo.
Nowadays these (though very dull and cheap looking) speakers can be had for only a few tenners.
Some other fairly affordable speakers that made me wonder if I got the price right (appr. €700,- a pair, but purely based on their performance double that price would be justified) are the Audio Note AX-two.
They look very plain, finished in a cheap looking, fake veneer, but boy o boy...they can sound truly amazing when partnered with the 'right' amp and source.
My most recent experience with some affordable speakers that (can) perform way better than their price would suggest is the little Dali Oberon 1.
The finish (eventhough the light-oak veneer is fake) is wonderful, they're not really fussy about placement and they're great for people who live in a small, noisy appartment, and listen mostly at modest/late-night volume levels. The Oberon 1's are open, fast and detailed. (the treble, eventhough sparkling and detailed can be a little spicey though, so the partnering components have to be chosen carefully)