Yeah, way over paid. I have a total of 6 RX 580's and 1 570. I never paid over $309 per card (most were at $299, the 570 was $229). I have a mix of XFX, Asus, MSI and PowerColor.  I'm getting right at or over 30 Mh/s on each card dual mining. I have a little more tweaking left to do on each to make sure the power and speed are optimal, but I'm pretty close right now.

At $500 a card, your ROI is going to be right at 5 months plus however long it will take you to pay off the rest of the system - so you're probably talking a 6 month ROI. Buying the cards at the right price, and you'll have an ROI of half that.