IF statemants

[georj]

i need some help with a major IF Statement i will try explain what i am
doing.
This is for costing development products
data is pulled in from an ERP system there are three table arrays
1.Warehouse, 2.Bread, 3.Veg
then we have a access datbase which has new ingredients which are on
trail the table array is Development.

a code is put in a cell eg 51043 a vlookup is done which several
columns will pull data in according to the code.
the column having problems with is the costs what i want it to do is
lookup to see if there is a last_cost if it is blank or 0 then do a
lookup at standard_cost and put the figure in
e.g of code i have written for certain cells
=+IF(ISNUMBER($C29),+IF(ISERROR(VLOOKUP($C29,Veg,4,FALSE)),"--->",VLOOKUP($C29,Veg,4,FALSE)),VLOOKUP($C29,Veg,5,FALSE)+IF(ISERROR(VLOOKUP($C29,Development,4,FALSE)),"--->",VLOOKUP($C29,Development,4,FALSE)))
and for other cells
=+IF(ISNUMBER($C33),+IF(ISERROR(VLOOKUP($C33,Warehouse,5,FALSE)),"--->",VLOOKUP($C33,Warehouse,5,FALSE)),+IF(ISERROR(VLOOKUP($C33,Warehouse,7,FALSE)),+IF(ISERROR(VLOOKUP($C33,Development,4,FALSE)),"--->",VLOOKUP($C33,Development,4,FALSE))))
and one which has to look at conversions
=+IF(ISNUMBER($C15),+IF(ISERROR(VLOOKUP($C15,Warehouse,6,FALSE)),
"--->",+IF(ISERROR(VLOOKUP($C15,Warehouse,5,FALSE)),+IF(VLOOKUP($C15,Warehouse,6,FALSE)
= "LOAF",VLOOKUP($C15,Warehouse,7,FALSE)/VLOOKUP($C15,Bread,5,FALSE),
VLOOKUP($C15,Warehouse,7,FALSE)),+IF(VLOOKUP($C15,Warehouse,6,FALSE) =
"LOAF",
VLOOKUP($C15,Warehouse,5,FALSE)/VLOOKUP($C15,Bread,5,FALSE),VLOOKUP($C15,Warehouse,5,FALSE)))),+IF(ISERROR(VLOOKUP($C15,Development,5,FALSE)),"--->",VLOOKUP($C15,Development,5,FALSE)))

if any one can help and point me in the right direction would be very
grateful. if need any more info please email.
thank you in advance Jason "going round in circles" George