The CARP IPs can be handed over from one firewall to the other. What happens in the background is that the failover node grabs the macadress of the CARP IP after the master has died, so nobody in the network will notece that actually another machine took over. same IP, same MAC. The LAN CARP IP that is used as the gateway will act the same.
The price for the nexcom is right. It has some benefits like serial redirection (you even can access the bios at com1) and a rather short 19" 1U case (many switches are even deeper). I configured a 1U mini ITX system with 4 nics and a via C3 1GHz cpu but ended up around the price of the nexcom, at least when using non crappy hardware. And the nexcom comes completely assembled even with serial cable. Add RAM, a cf-card or a hdd and you are ready to roll.