As someone who used to own Polk rTI series speakers and purchased SVS-SCS speakers to replace them, I recommend spending more. The SVS speakers were noticeably better better sounding speakers and definitely fit into your budget.
If you do end up buying the Polk speakers, spend more on their center channel and make sure you don't buy a Polk subwoofer. For subwoofer, stick with SVS, HSU, eD, etc.