For some special app I need a rugged/industrial router, but low cost. Following minimum specs:
8MB flash, 256MB RAM, 11g, USB, 1 WAN, 1 LAN, TF/SD-card, internal 3g modem. Official openwrt support.
Optional: 11a.
So a highest end, MT7620A based device would be minimum; MT7621 would be best.
Any suggestions ?
ZBT WG3526 or UniElec U7621-06 are the ones that I could think of from the top of my head.
They have options of 256/512 MB RAM, 16/32 MB Flash, a Quectel EC25 (3G/4G) card added along with WiFi. Should cost less than USD 100 and available on AliExpress.
Unfortunately, both of them look like office type devices, not rugged ones.
I tried to mention MT7621 devices closest to the hardware config you were looking for.
Apart from a high operating temperature range, are you looking for devices suitable in high vibration environment as well?
See if V7 Espressobin is a better device for you https://www.globalscaletechnologies.com/p-79-v7-marvell-espressobin.aspx
Rugged: Referring to vibration, temperature, dust. Solid case.
By far the most available ruggedized devices will be mini pcs. Since you don't really need a lot of CPU power, you could go with any of the cheap j1900 based rugged mini pcs like the Qotom etc. They'll have about 10 times the RAM and 1000x the flash of what you need, but I'm sure you'll think of something to do with that 
Edit: to get the internal 3G modem you'll have to identify one with an expansion slot and an appropriate mini pcie 3G card.
Why not mount a cheap OpenWRT device inside a rugged IP68 rated case?
Inexpensive small-form factor devices such as the OpenWRT proven TP-LINK WR703N or TL3020, provide all the functionality you ask apart from the 3G connection > but you can fit a USB 3G or faster 4G dongle on the USB port. Inside an IP68 rated [plastic] box, a router is impervious to even salt spray. Obvioulsy power supply is through waterproof glands.
I'm not endorsing any of the products here, but you'll get the idea of the rugged enclosures available : https://www.data-alliance.net/enclosures/
edit + Tip: Remove a router from it's plastic case and mount the PCB inside the enclosure - this improves heat dissipation. To ruggedize further, solder in the power connection.
No OpenWrt support for above device found in the ToH. First time poster and content say the above is likely more spam.
While I personally err away from these simply due to the "non-outofthebox" nature..... ( strange thing for me... bacause everything I own has been ripped apart..... go figure ...... ) when I consider rugged.....
I'd choose a RasPi or whatever other SBC is cheap and well supported...... ( i think ^ @codemarauder 's suggested esspressobin fits that well )
One that ran on the cooler side too preferably, cause the custom enclosure would likely cramp him up a bit......
One of those waterproof cases and your rugged less the power supply......
Did you find a suitable product? I am looking for something with similar requirements but while cellular would be a nice to have it is not required.
thx, have you had good results? What kind of use case is it for?
Which build of openwrt are you using on your ZBT-WG259?
Sorry but no details cause commercial project.
Sorry to tag up on this earlier thread, but is ZBT-WG259 compatable with 802.11w protocols?
Having trouble finding info online. Thanks!