Make names of first, second and third table as sku, acct_type and
Cont_typ.
And name last table that include price as Price.
Then, I thought that it is worth to try following Query.

While I have no environment of AS/400 or iSeries to try it,
I couldn't find no inconsistency with syntax by referencing "DB2
Universal Database for iSeries SQL Reference Version 5 Release 2".

[code]WITH prf_Price (sku, price, match_level) AS (
SELECT P.sku, P.price
    , CASE
      WHEN P.Cont_typ = C.Cont_typ
       AND P.acct_typ = A.acct_type THEN
           1
      WHEN P.Cont_typ = C.Cont_typ
       AND P.acct_typ = '' THEN
           2
      WHEN P.Cont_typ = ''
       AND P.acct_typ = '' THEN
           3
      END
 FROM Cont_typ  C
    , acct_type A
    , sku       S
    , Price     P
WHERE A.acct_prf = C.acct_prf
  AND S.acct_prf = A.acct_prf
  AND S.acct_no  = A.acct_no
  AND P.sku      = S.sku
)
SELECT sku, price
 FROM prf_Price PP
WHERE match_level
      = (SELECT MIN(match_level)
           FROM prf_Price PM
          WHERE PM.sku = PP.sku
        )
;[/code]