a lot of people have good luck with wifi router load openwrt, a common one is TP-Link TL-WR703N.
TP-Link TL-WR703N
CPU Atheros AR7240 400Mhz
802.11 b/g/n 150Mbps (130Mbps real)
4 MB flash memory
32 MB RAM
USB 2.0 port (High-Speed only, use an external High-Speed hub for Full/Low-Speed devices)
TP-Link TL-WR703N cost 90.00 RMB/15.00 USD at Chinese market, You could get it from ebay for 20.00 USD
TP-Link TL-WDR3600
Ethernet: Atheros AR8327N Gigabit Switch
CONCURRENT DUAL BAND WIRELESS 2.4GHz 300Mbps+5GHz 300Mbps
CPU AR9344 (MIPS)/560 MHz
USB 2 x 2.0
8MB flash memory
128 MB RAM
Power Suply 12V/1.5A
I got mine for 40.00 USD from newegg onsale few weeks back, It run openwrt with arduino very well.