well i would look into Conjured Entertainment's money script you can get it here
http://forum.thegamecreators.com/?m=forum_view&t=130281&b=24
but to make the counter count down i suggest that you use a trigger zone and a narrow hallway from when you want your timer to start. put this into the trigger zone
;Artificial Intelligence Script By Conjured Entertainment
;Header
desc = start clock countdown timer
;Triggers
:state=0:hudreset,hudx=50,hudy=20,hudimagefine=gamecore\text\user\pickedup1k.dds,hudname=itemprompt1k,hudhide=1,hudmake=display,state=10
:state=10,plrwithinzone=1:globalvar=1,incvar=1000,coloff,activateifused=13,activate=2,plrsound=audiobank\misc\ping.wav,hudshow=itemprompt1k,hudfadeout=itemprompt1k,state=1
:state=1,activated=2:globalvar=1,decvar=1,activateifused=13
;End of Script
try to see if this works and tomorrow i will make a HUD that says timer for you.