Shung you've got me jealous, a Colt M4 for $1800, that just ticks me all kinds of off for us living here in the U.S., and I bet it's a post 87 to boot. If there was a pre-87 available here in the U.S. it'd probably go for $18,000. Good luck on that vote you have coming about the Sig 556.
Cheapest, Ruger Blackhawk .44 Magnum $150
Expensive, CETME $550 (first EBR I ever bought and have learned to get them cheaper since, still a great shooter)