perl

my $i = 0 ;
my %h = map{ $_, $i ++ } split //, '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%';
my %hr = reverse %h ;

print $hr{ +( eval join '+', map{ $h{$_} } split //, 'PIYOPIYO'  )  % 43 } ;

アホだ、ダブルコーテーションになってた。変数展開するじゃん。

VBA

Function modulus43(ByVal d As String)
    Dim str As String
    str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%"
    Dim i As Integer
    Dim j As Integer
    Dim o As Integer

    For i = 1 To Len(d)
        For j = 0 To 42
            If Mid(d, i, 1) = Mid(str, j + 1, 1) Then
                o = o + j
                Exit For
            End If
        Next j
    Next i
    modulus43 = Mid(str, (o Mod 43) + 1, 1)
End Function

適当なセルにて =modulus43(A1) とかする、、、

ruby

a = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-. $/+%".split("") 
h = (a).zip(0...a.size).to_h 
hr = h.invert
p hr[ "PIYOPIYO" .split("").map{|x| h[x] }.inject(:+) % 43 ]

.to_h は、ruby 2.1 からだそーで。