Cost Effective Router

Hi Experts, 

I am in search of a Controller/SOC or processor which is indeed cost effective and on top of which I can have router functionality. Basically I want to interface a Telit DE910 Cell module via USB to this solution. 

So the product will thus be a Cell Modem Router that should have 1 WAN and 2 or more LAN ports. 

Which routing protocols should I look forward for? 

Is there any suitable RTOS which is opensource and router source code is available? Should I be looking for full-fledged Linux or something like openwrt or vxworks? 

Kindly suggest your expert advices. 

Thank you, 

Rahul Shah