accessing an excel sheet from multiple other workbooks.

I have an excel sheet calculating cost for various parts. There are
many versions of this sheet (different one for each part number). I
want all of these sheets to pull some common parameters from one
master sheet. This way when these parameters need changed, it must
only be done one time. Then all other sheets can be updated.

The problem I'm having is that all these excel files while all in the
same common folder, are also divided up in subfolders. Is there
generic method I can use so they will find the file to import from
regardless of whether the master file is in the same folder, a folder
above, or even two folders above? (i.e. I only want to have one copy
of the master sheet with variable parameters, and not have to make a
copy of it inside each individual folder also.)

Any help or suggestions will be very appreciated.