I actually managed to find a function to pull the data depending on the
variables selected:

DGET(master!$A$1:$F$8,B12,$A$5:$C$6))

I'm really stuck with the selection drop down menus. I've managed to kind of
get something to work with OFFSET for var2 (except that the options displayed
in the drop down menu may not be unique)

=OFFSET(data_start,MATCH(A6,var1_column,0)-1,1,COUNTIF(var1_column,A6),1)

I have no idea on how to apply this to var3 to make it dependent on
selections from var1 and var2. I'm not sure whether this is the right
direction to go into.