What sounds reasonable? Based on the information on their website, www.taccom3g.com;
A complete upper assembly, with a buffer plug, is approx $518 after shipping
Just the barrel, BCG and plug is approx $343 after shipping
A 5% or 10% GB discount (not really sure what their overhead is, and what they can afford) would be in the neighborhood of $493-$472 for the complete upper, or $327-$312 for the basic builder parts.
This is just a "ballpark" figure/estimate that I came up with, and is in NO WAY based on any conversation with Taccom.... I haven't even tried to contact them yet. This is strictly for interest purposes.