Apple Logic Pro /LogicExpress Discussion

Sorry, this isn't a strictly Logic query, but I am looking for  
monitors to use with logic, which I am running on my imac:

  Model Name:	iMac
   Model Identifier:	iMac9,1
   Processor Name:	Intel Core 2 Duo
   Processor Speed:	2.93 GHz
   Number Of Processors:	1
   Total Number Of Cores:	2
   L2 Cache:	6 MB
   Memory:	4 GB
   Bus Speed:	1.07 GHz
   Boot ROM Version:	IM91.008D.B00
   SMC Version (system):	1.37f3

I was told by an audio engineer that you need to spend £400 a speaker  
or its money down the drain, which rather made me gulp (I guess that's  
about $400) so I did some research and got totally and utterly  
confused. In the end the speakers that I guessed might be best are these

http://store.solutions-inc.co.uk/product/krk-rp8-g2-monitors-pair

The KRK RP8 from Rokit

I would anticipate having them about three feet away from me, in a  
room that is about 12' x 20'. I don't have a studio to work in, and  
the room has wooden floors and lots of windows. That, I know, is far  
from ideal but there's not much I can do about it.

Given that, does anyone have any advice as to what speakers I should  
get. I don't even know if the ones above are right for using with an  
imac, so any help would as always be much appreciated

thanks in advance

Andy