If you're using Excel 2013 you can use the IFNA function.

Entered in D5 and copied down:

=IF(B5="","Unit",IFNA(VLOOKUP(B5,Prices,2,0),""))

Entered in E5:

=IF($B5="",0,IFNA(VLOOKUP($B5,Prices,COLUMNS($E5:E5)+2,0),""))

Copy across to G5 then down as needed.