My friends and I would like to set up a VPN between several homes
througout our city. We are looking for a solution that allows us to
have a VPN box/router plugged into our standard router. We want all
the VPN activities to occur on this device, so that one can plug into
it and be on the VPN without any additional clients, certs,
configuration. We currently use WASTE, but we find it awkward
(limited/no scripting support). We'd like to just plug a new box into
the VPN device, and bam, DHCP hands you an address on our VPN.

What solutions exist? Do we need a central concentrator? Is this even
possibe? We are looking to spend no more than ~$500/node with around
10 total nodes (homes).

Ideally each node would have a topology like this:

internet -> cable modem -> router -> vpn device -> hosts on vpn (10.x.x.x)
                                  \
                                   -> other hosts not on vpn (192.168.x.x)