TP-Link WR703N is a popular low cost router well supported by OpenWRT that costs about $23 shipped. But there’s now a new cheaper router that’s been mentioned in comments on CNX Software a few times, with a different processor, but otherwise similar specs plus an extra Ethernet port. NEXX WT1520 is powered by Mediatek RT5350F, sells for $15 including shipping from sites like Banggood, Aliexpress and eBay, and can run OpenWRT, although it’s not officially supported yet.
- SoC – Mediatek (previously Ralink) RT5350F MIPS processor @ 360MHz
- System Memory – 32MB RAM
- Storage – 4MB NAND flash
- Wi-Fi 802.11b/g/n up to 150 Mbps with built-in PIFA antenna
- 2x 10/100M Ethernet (LAN and WAN)
- USB – 1x USB 2.0 host port, 1x micro USB port for power
- Misc – Status LED, reset pinhole, power button
- Power – 5V via micro USB port
- Dimensions – 63 x 43 x 17mm
- Operating temperature – 0 – 40 C
Some shops can the router WT1520F, while others WT1520H, or even just WT1520, and I’m not sure if there are differences between the two or three models. The router has already been teared down, and serial port connected as shown in the picture below (Source: OpenWRT Wiki).
GPIOs do not seem to be easily accessible, so in case you need I/Os or/and an even smaller form factor, you’d probably be better off with something like Vocore + Dock that currently sells for $45 with a serial board, as well as a larger NAND flash.