The best sub out there for the price is the monoprice monolith 10”. It’s $500 and competes with $1200 subs.
Also, if you go with Polk, you want the newest generation from them. The previous series were terrible, even for the price (minus the FXi which was their previous top-end for surround speakers). Check Polk’s official eBay page as they sell returned/open-box/refurbished speakers for dirt cheap (90-day return policy too, and I think a 1-year warranty). For floor standing and center speakers you’d want Polk’s S series, which is what I went with (S30 center, S50s for floor), and they sound great (better than the more expensive Klipsch that they compete with, which I demo’d at BB prior to making the decision).