you don't mention the version of MFG/PRO you are using
(assuming you are using eB2.1 version)
cost method (per site) is defined in menu 30.9 Cost Set to Site Assignment
for Inventory valuation, GL cost set is used
in this example, replace mysite & mypart with your values
Code:
assign costset="" cost=0.
find first si_mstr where si_domain = global_domain and si_site = mysite
no-lock no-error.
if si_gl_set<>"" then costset=si_gl_set.
else do:
find first icc_ctrl where icc_domain = global_domain no-lock no-error.
costset=icc_gl_set.
end.
find sct_det where sct_dom = global_domain
and sct_site = mysite
and sct_sim=costset
and sct_part = mypart
no-lock no-error.
if available sct_det then assign cost=sct_cst_tot.