Really at the end of the day your amplification also plays a part [ large ] in your speaker performance. If your only using an AVR the best // worst speakers are going to sound crap. [ducks for cover]
B & W speakers are very selective on there amplification, Some might say an acquired taste, to get the best performance, Especially with the 800 series. I know of people that have spent an absolute fortune on amp's. and where still not happy with the performance or there top of the range 800 series.
Really with your low budget, I would not even consider B & W, unless your looking at small bookshelf speakers, And while you might consider used / 2nd hand, your also buying there reason for selling in the first place. Regardless of what you end up with if there used, insist you hear them and take notice of what amp;s there using, No audition No sale