That's a reasonable amount for a bookshelf based home theater setup (especially since the sub isn't included). The current Yamaha speakers you have are average at best. If you're sticking to 5.1 you can get some pretty good speakers for your money. These are the following bookshelf speakers which should fit within your budget (partnered with their respective center and surrounds):
B&W 685s2
Dali Opticon 1
Dynaudio Emit M10
Focal Chorus 706
KEF Q300
Monitor Audio Silver 1
PSB Imagine XB
Q Acoustics Concept 20
SVS Ultra bookshelf
Tannoy Revolution XT mini
I'm sure there are other speakers too but these are the ones that come to my mind. Of the lot,
I'm biased to the B&Ws. Audition (preferably with a Yamaha amp/receiver) and choose the ones you like the most. After all it's your ears and what sounds best to you is all that matters