If you are just using IP on the WAN side, it might be an option to use the WAN interface of the CS410 for the public IP. Then you just need a hub/switch to connect the WAN to the router and the CS410. Then the CS410 will use one public IP address (and a private IP address, make sure it is a static one to avoid problems with the default IP gateway) and the router will use another public IP address. However in this setup, QoS will remain a problem.
In the ultra-low cost segment, I only know about OpenWRT project where you essentially load Linux on the router. That gives you a lot of options if you are able to setup Linux routing.
We did search for low-cost router solution some time ago. In the end we gave up on it and bought a standard Cisco router on eBay.