Funny as it is, this is exactly the spec number for Cisco Meraki MX60 with stock firmware:
The MX60 passed its end of support in October, so companies that had those units are purging them left and right, and they are available very inexpensively. And, believe it or not, there's a guide for that, too:
[HOWTO] Installing OpenWrt on Cisco Meraki MX60
The downside is, the installation process is quite a bit more involved; you will need to open the case, use a special kind of cable called UART, and set up a TFTP server.