I customized a spreadsheet I want all users on my project to use.

I'm not in IT and my IT dept. is just a bit lame in getting me an answer as
to exactly what I must do to let my vba workbook run without forcing users
to lower their security or be asked every time if they trust the thing to
run macros. From what research I've been able to do, it seems their are
certificates you can buy from thawte or verisign that do this, but I'm still
confused. Can anyone tell me:
1) the cheapest signature I can get that will do what I'm looking for
2) tell me how to tell IT to make it available
3) how I make code updates to the spreadsheet (I tried emailing just the
modules to the office, but that didn't get far

Why is this so damn confusing?? Is there a guide that explains this clearly
with less than a half hour of effort??

A zillion thanks for help!