What do BT, Ray Charles, and Carlos Rios have in common? They all use M-Audio BX-5s in their home studios and praise them. In fact, in a recent interview in Keyboard, BT raved about how his BX-5s (with an M-Audio sub) are knocking out his friends with $10K monitoring systems. He swears that he'll never leave them--yeah, right, but still, not a bad endorsement for a little budget monitor.
I bought mine for $250/pair and agree, with one stipulation. I've found these little BX-5s to provide wonderfully clear and smooth highs and mids, and the inclusion of a sub knocks them out of the sonic ballpark. Without the sub, the bass is adequate for me to produce solid mixes, but I suspect it would be too light for mixing some types of bass-heavy music. I've found the same to be true for any monitors sporting a 5" cone. (I've read recent reviews of the 5" Tapco, Fostex, and Event--and the writers reached the same basic conclusion for all of these smaller speakers.)
But if you can live with a bit lighter bass but need a small footprint, then these M-Audios are worth a look and listen. You can always add a hidden sub later when the money's available.
My biggest tip is to do what I did: buy 2-3 top models that you're considering and try them in *your own studio space*. When I did this, the M-Audios won clearly for me, especially with their subtle, adaptable EQ trimming--a nice feature if you're not able to change the room much. (My studio doubles as a dining room, and my wife promptly nixed the idea of foam baffles and partitions even though I thought they'd look cool--like dinner in Disneyland.)
Good luck, whatever you decide,
J.