Try:

=IF(LEFT(A1)="<","<","")&SUBSTITUTE(A1,"<","")*B1*8.34

or

=IF(LEFT(A1)="<","<"&MID(A1,2,10)*B1*8.34,A1*B1*8.34)

The latter will keep the numbers as numbers instead of convert to text if the column A cell doesn't have a "<".