Wharfedale 8.2As may be a little bit out of your price range ($340), but I have them and so far I haven't had an issue with translation. Though I should say that I haven't fully tested them yet. But the few mixes I've done sound as right on any other system as they do on the Wharfes. Not that my mixes are good, just that the crap translates well .
For £150 perhaps a pair of Tannoy reveal active from ebay.
I got a pair very cheap locally a few days ago and think they sound quite good, though i haven't tested how they translate.
...M-Audio BX5as, although saying that one of mine just recently packed up. Lovely sound though (atleast to my ears - I had been monitoring through a HiFi previously). Got mine for £120 inc. VAT from Sound Control in Birmingham