Well, Ray, this is a virtual HR. We aren't really posting.
OT: Must agree with Jimmy. THE most important thing I did to date; great monitors, nice equipment, more practice time (well that helps a lot, too), etc. was treat my room. With good treatment and good skills, mixing becomes easier, getting better skills becomes easier, improving your ears becomes easier. When your room lies to you and exaggerates certain frequencies and hides others, $10,000 monitors just become better tools for lying to your ears...
That said, I still believe Mike had it right in the other thread. Get some decent monitors and then stick up your treatment. DIY treatment will run you about 10-20 quid per panel if you're handy (4x24x48, sorry, don't know mm). You can do them six at a time (cheapest to buy in 12-2"x24x48 packs) + wood, cloth and mounting (green cement helps, too) and you can do a normal sized room (including building your own superchunks in the corners for about your 300-400 quid budget. I spent $1500 on some "kits" that included the precut sheets or 703 (705 in the corners), prebuilt frames and precut cloth with mounts and green glue. 24 panels + 2 ceiling clouds + corner bass traps (I went 6", but I'm going to redo the two corners with superchunks when (if) I can afford it. My room has doors in the corners on the back wall, so I needed the mountable kit to hang in the ceiling/wall intersection instead of being able to put them in the wall to wall corners (that should make sense, but knowing me it probably didn't).
Definitely go with Roxul or OC 703/705 and don't bother with the useless foam that is sold so prominently...in a pro studio, with perfect dimensions, those may have some bearing, but in our imperfect little rooms, foam just doesn't make the grade.