My low-cost workhorse is ZBT WE826. Have done various hotspot projects with it (incl. coova-chilli), for various companies. The good part is, the WE826 (standard version) has ample resources (128MB RAM) for low(est) price. Also SD-card is possible, for swap or mass storage.
I also used GLis for various projects. They are good, too, but a bit more upscale in price, especially when comparing the hardware (RAM !). openwrt is constantly growing, so 128MB gives you more freedom for the future or functionality, like remote firmware upgrades, VPN etc.
Disclaimer: I am not affiliated with ZBT 