C:\@Work\Perl\monks\dani_cv>perl -wMstrict -le
"use Text::LevenshteinXS qw(distance);
 my $base = shift;
 print qq(\noutput:);
 for my $try (@ARGV) {
   my $no = acquired_1_dollar($base, $try) ? q{} : q{NO };
   print qq{$base <> $try: ${no}match};
   }
 sub acquired_1_dollar {
   my ($base, $try) = @_;
   return $try =~ m{ \$ }xms && distance($base, $try) == 1;
   }
"
test.ext
$test.ext  te$st.ext  test$.ext  test.$ext  test.e$xt test.ext$
$est.ext  te$t.ext  tes$.ext  test$ext  test.$xt  test.e$t  test.ex$
test.ext  tost.ext  te$t$.ext  tet.ext  t$t.ext  tes$t$xt test$e$t
""  $  test  wertyu  wert$yu  w$er$tyu

output:
test.ext <> $test.ext: match
test.ext <> te$st.ext: match
test.ext <> test$.ext: match
test.ext <> test.$ext: match
test.ext <> test.e$xt: match
test.ext <> test.ext$: match
test.ext <> $est.ext: match
test.ext <> te$t.ext: match
test.ext <> tes$.ext: match
test.ext <> test$ext: match
test.ext <> test.$xt: match
test.ext <> test.e$t: match
test.ext <> test.ex$: match
test.ext <> test.ext: NO match
test.ext <> tost.ext: NO match
test.ext <> te$t$.ext: NO match
test.ext <> tet.ext: NO match
test.ext <> t$t.ext: NO match
test.ext <> tes$t$xt: NO match
test.ext <> test$e$t: NO match
test.ext <> : NO match
test.ext <> $: NO match
test.ext <> test: NO match
test.ext <> wertyu: NO match
test.ext <> wert$yu: NO match
test.ext <> w$er$tyu: NO match