D-link dir-862l new-open box on eBay... It goes from ac1600 to ac1750 on dd-wrt. It uses the same internals as the tp-link c7 and is regularly available for ~$30-40, and sometimes cheaper if you're patient.
If you want a more powerful SoC and a usb3 port, the netgear ac1450 shows up refurbished from time to time for ~$60 on sites like newegg. I've had one for about a month now. I wasn't sure about buying into broadcom, as I've been quite happy with atheros, but all is well so far. Wireless settings are just a bit different. It is also nerfed in the stock firmware and becomes ac1750 on dd-wrt. It has a dual core 800mhz arm processor.