some are overrated, others are not, better go with opti line. If you need class D amps the you use opti line, heritage 2600d, vibe 1200d or vibe 1800d. Those are the most reliable for mono.
They need power, frequency control and a good enclosure. The name on the amp has little to do with it. Expensive amps defintitely have their benefits, but "good subs need them" isn't one of them.
That being said - To really make those subs sing they're going to need close to 1000w rms a piece. That means an amp that's close to 2000w at 1 ohm. That isn't doable on your budget.
The Vibe 1800D would be around 600w per sub, the heritage 2600d is a bit more - probably what I would recommend since they're about the same price.
Within your budget the only other option that comes to mind is the Hifonics bx1605 at onlinecarstereo.com which is appx. the same power as the 2600d.