Well I think I have it working now - must have been a syntax error on my part. Here is my formula if others are interested:
if (price eq "1") then
subtotal = (sqinches * .18)
elseif
(price eq "2") then
subtotal = (sqinches * .19)
elseif
(price eq "3") then
subtotal = (sqinches * .20)
etc...
endif