You should be able to use any standard home gateway (CPE). We have used Linksys devices, but any device that can be flashed with OpenWrt should work. The only extra work the B4 does is to encapsulate IPv4 traffic in IPv6 and that happens at the kernel level. If the CPE can handle normal cable/DSL traffic, it can handle DS-lite.
The AFTR element can run on any Linux box, even a netbook. The AFTR code runs in user mode. There is a context switch for every packet in or out, so the limiting factor is CPU. If you want better performance, consider using something better than a netbook. :)