The Audire Otez can be found at the top of your budget. It’s not pretty, but it’s a powerhouse that sounds absolutely wonderful. Mine has dislodged McIntosh monoblocks among many other fine, higher dollar amps. This amp drives the hell out of my ADS L2030’s. While they’re more efficient and an easier load than your Infinities, I don’t think it’ll break a sweat given it can double down all the way to 800 wpc at 2 ohms.
There’s one on Reverb now that I know can be had just over your budget (~$1000 + shipping). Might be able to find another one for less if you’re patient, but they don't come up for sale very often.