Uiua, score 2, 85 73 56 bytes

reduceaddnotmemjoionnegaaddstringifyA ranfloaddpipowpi e

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Requires an # Experimental! comment at the beginning.

Formats to /+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e.

Explanation

/+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e
                     ⌊+πⁿπ e pushes 26
                    ⇡        gets all whole numbers less than 26
         stringifyA          pushes "A"
        +                    shifts "A" by each of [0 1 2 3 ... 25], resulting in the uppercase alphabet
    ⊂⟜¯                     joins the array with itself lowercase
  ¬∈                         checks for each element in the original string whether it's NOT in that array
/+                           get the sum of the elements

Uiua # Experimental!, score 0, 85 73 56 51 bytes

firunwhememdipabsaddranceipowetaaddtauetastringifyA

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Formats to ⊢°⊚∈⊙⌵+⇡⌈ⁿη+τηstringifyA.

Uiua, score 0, 85 73 56 bytes

reduceaddnotmemjoionnegaaddstringifyA ranfloaddpipowpi e

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Requires an # Experimental! comment at the beginning.

Formats to /+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e.

Explanation

/+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e
                     ⌊+πⁿπ e pushes 26
                    ⇡        gets all whole numbers less than 26
         stringifyA          pushes "A"
        +                    shifts "A" by each of [0 1 2 3 ... 25], resulting in the uppercase alphabet
    ⊂⟜¯                     joins the array with itself lowercase
  ¬∈                         checks for each element in the original string whether it's NOT in that array
/+                           get the sum of the elements

Uiua, score 2, 85 73 56 bytes

reduceaddnotmemjoionnegaaddstringifyA ranfloaddpipowpi e

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Requires an # Experimental! comment at the beginning.

Formats to /+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e.

Explanation

/+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e
                     ⌊+πⁿπ e pushes 26
                    ⇡        gets all whole numbers less than 26
         stringifyA          pushes "A"
        +                    shifts "A" by each of [0 1 2 3 ... 25], resulting in the uppercase alphabet
    ⊂⟜¯                     joins the array with itself lowercase
  ¬∈                         checks for each element in the original string whether it's NOT in that array
/+                           get the sum of the elements

Uiua, score 0, 85 73 bytes

reduceaddnotmemflipjoionnegaaddstringifyA ranaddfloetaunsqraddceipifloeta

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Requires a # Experimental! comment at the beginning.

Formats to /+¬∊:⊂⟜¯+stringifyA ⇡+⌊η°√+⌈π⌊η.

Explanation

/+¬∊:⊂⟜¯+stringifyA ⇡+⌊η°√+⌈π⌊η
                      +⌊η°√+⌈π⌊η pushes 26
                     ⇡           gets all whole numbers less than 26
          stringifyA               pushes @A
         +                         shifts @A by each of [0 1 2 3 ... 25], resulting in the uppercase alphabet
     ⊂⟜¯                          joins the array with itself lowercase
  ¬∊:                              checks for each element in the original string whether it's NOT in that array
/+                                 get the sum of the elements

Uiua, score 0, 85 73 56 bytes

reduceaddnotmemjoionnegaaddstringifyA ranfloaddpipowpi e

Try it here!

Requires an # Experimental! comment at the beginning.

Formats to /+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e.

Explanation

/+¬∈⊂⟜¯+stringifyA ⇡⌊+πⁿπ e
                     ⌊+πⁿπ e pushes 26
                    ⇡        gets all whole numbers less than 26
         stringifyA          pushes "A"
        +                    shifts "A" by each of [0 1 2 3 ... 25], resulting in the uppercase alphabet
    ⊂⟜¯                     joins the array with itself lowercase
  ¬∈                         checks for each element in the original string whether it's NOT in that array
/+                           get the sum of the elements