Python 3 + astor, 1017 bytes - (25 + 50 + 100) = Score: 842

edit: I am unable to test the ridiculously long integer (1234567891234567891234564789087414984894900000000) but from my knowledge, Python 3 supports arbritrarily long integers.

from ast import*
from astor import*
ts,nt,bo,m,d,a,s,n,p,ty=to_source,NodeTransformer,BinOp,Mult,Div,Add,Sub,Num,parse,type
class M(nt):
    def visit_BinOp(t,z):
        if ty(z.left)==bo and ty(z.right)==bo:return bo(t.visit_BinOp(z.left),z.op,t.visit_BinOp(z.right))
        if ty(z.left)==bo:return bo(t.visit_BinOp(z.left),z.op,z.right)
        if ty(z.right)==bo:return bo(z.left,z.op,t.visit_BinOp(z.right))
        if ty(z.op)==m:return n(z.left.n*z.right.n)
        if ty(z.op)==d:return n(z.left.n/z.right.n);return z
class A(nt):
    def visit_BinOp(t,z):
        if ty(z.left)==bo and ty(z.right)==bo:return bo(t.visit_BinOp(z.left),z.op,t.visit_BinOp(z.right))
        if ty(z.left)==bo:return bo(t.visit_BinOp(z.left),z.op,z.right)
        if ty(z.right)==bo:return bo(z.left,z.op,t.visit_BinOp(z.right))
        if ty(z.op)==a:return n(z.left.n+z.right.n)
        if ty(z.op)==s:return n(z.left.n-z.right.n);return z
class S(nt):
    def visit_Num(t,z):return n(sum(map(int,list("".join(map(str,range(1,z.n+1)))))))
print(ts(S().visit(A().visit(M().visit(p(input()))))))

Python 3 + astor, 1017 1007 bytes - (25 + 50 + 100) = Score: 842 834

saved 10 bytes by removing ts and changing p

edit: I am unable to test the ridiculously long integer (1234567891234567891234564789087414984894900000000) [hangs my computer] but from my knowledge, Python 3 supports arbritrarily long integers.

from ast import*
from astor import*
nt,bo,m,d,a,s,n,p,ty=NodeTransformer,BinOp,Mult,Div,Add,Sub,Num,map,type
class M(nt):
    def visit_BinOp(t,z):
        if ty(z.left)==bo and ty(z.right)==bo:return bo(t.visit_BinOp(z.left),z.op,t.visit_BinOp(z.right))
        if ty(z.left)==bo:return bo(t.visit_BinOp(z.left),z.op,z.right)
        if ty(z.right)==bo:return bo(z.left,z.op,t.visit_BinOp(z.right))
        if ty(z.op)==m:return n(z.left.n*z.right.n)
        if ty(z.op)==d:return n(z.left.n/z.right.n);return z
class A(nt):
    def visit_BinOp(t,z):
        if ty(z.left)==bo and ty(z.right)==bo:return bo(t.visit_BinOp(z.left),z.op,t.visit_BinOp(z.right))
        if ty(z.left)==bo:return bo(t.visit_BinOp(z.left),z.op,z.right)
        if ty(z.right)==bo:return bo(z.left,z.op,t.visit_BinOp(z.right))
        if ty(z.op)==a:return n(z.left.n+z.right.n)
        if ty(z.op)==s:return n(z.left.n-z.right.n);return z
class S(nt):
    def visit_Num(t,z):return n(sum(p(int,list("".join(p(str,range(1,z.n+1)))))))
print(to_source(S().visit(A().visit(M().visit(parse(input()))))))

Python 3, 1017 bytes - (25 + 50 + 100) = Score: 842

Python 3 + astor, 1017 bytes - (25 + 50 + 100) = Score: 842

M(NodeTransformer|nt) - converts multiplication and division into their results.
A(NodeTransformer|nt) - converts addition and subtraction into their results.
S(NodeTransformer|nt) - converts numbers into their sum of digits via the Pythonic way.

M(NodeTransformer|nt) - converts multiplication and division into their results.
A(NodeTransformer|nt) - converts addition and subtraction into their results.
S(NodeTransformer|nt) - converts numbers into their sum of digits via the Pythonic (naïve) way.