Coslie from steam forums did some research:
http://steamcommunity.com/app/250520/discussions/0/1291817837625196247/ (http://steamcommunity.com/app/250520/discussions/0/1291817837625196247/)
As of Version 1.0.2.4
For -most- items :
The value of an item equal the sum of it's parts times a multiplier.
Multiplier varies by item type, and sometimes by the number of optional parts.
The specific part is irrelevant, the only thing that matters is the value.
I did not look at consumable items, their costs seem to be fixed and arbitrary.
Optional parts 0 1 2
Leather 2.25 2.25 2.5
Tac Vest 3 3 3.6
Riot 3 3 3.6
Helmet 2 N/A N/A
Metal* 3.3 < 3.3 <3.3
Boots** 2 2 N/A
Chem Pistol 3 N/A N/A
Energy Pistol 2 2 2
Psi 2
Taser 2 N/A N/A
Shield*** 1.5
Pistol 3 3 3.6
SMG****
A/R****
Sniper****
X-bow 3 3 3.6
Glove 2 2 2
Hammer 2 2 2
Knife***** < 1 <1 <1
Sry for bad formatting. Check steam thread for better one.