Neall wrote...
....
I am using this;

=IF(ISERROR(INDEX('Value Unit Prices'!C22:N41,
MATCH(C29,'Value Unit Prices'!A22:A41,0),
MATCH(Pricelevel,'Value Unit Prices'!D21:N21,0))*P29),"",
(INDEX('Value Unit Prices'!C22:N41,
MATCH(C29,'Value Unit Prices'!A22:A41,0),
MATCH(Pricelevel,'Value Unit Prices'!D21:N21,0))*P29))

This may work, but it's unlikely you either need to check for error
values in P29 or would benefit from trapping such errors of they
exist. I'd guess you only need to trap C29 not in 'Value Unit Prices'!
A22:A41 or PriceLevel not in 'Value Unit Prices'!D21:N21. If so, it'd
be more robust to use

=IF(COUNT(MATCH(C29,'Value Unit Prices'!A22:A41,0),
MATCH(Pricelevel,'Value Unit Prices'!D21:N21,0))=2,
INDEX('Value Unit Prices'!C22:N41,
MATCH(C29,'Value Unit Prices'!A22:A41,0),
MATCH(Pricelevel,'Value Unit Prices'!D21:N21,0))*P29,"")

Which works perfectly however PriceLevel can be changed so I have a cell
called leveloveride I want *include in this formula, basically if
leveloveride is not null that the formula is to use the level in leveloveride
in its equation, if leveloveride is 'null' the formula is to use Pricelevel
in its equation.

Change current references to PriceLevel to IF(ISBLANK
(LevelOveride),PriceLevel,LevelOveride).