my %value_lkup = (
    A => '1000',
    B => '2000',
);

my $pat = '[' . join('', keys %value_lkup) . ']';
s/($pat)/$value_lkup{$1}/g;

##</code><code>##

s/([AB])/ ( ord($1)-ord('A')+1 )*1000 /eg;