Is there a relatively quick program out there to accomplish at least the basics of this? Just a few regexes? I'm willing to do some manual conversion, but this is a pretty big set of scripts.

You can translate JavaScript to Python using Js2Py. It supports whole JavaScript and you can use it to translate large JavaScript modules like esprima.js (a JavaScript 6 parser).

>>> import js2py
>>> f = js2py.eval_js( "function $(a) {return a + arguments[1]}" )
>>> f
function $(a) { [python code] }
>>> f(1, 2, 3)
3

This is how the translated function looks like internally (it's rather ugly):

>>> print js2py.translate_js( "function $(a) {return a + arguments[1]}" )
from js2py.pyjs import *
var = Scope( JS_BUILTINS )
set_global_object(var)
# Code follows:
var.registers([u'$'])
@Js
def PyJsHoistedNonPyName(a, this, arguments, var=var):var = Scope({u'a':a, u'this':this, u'arguments':arguments}, var)var.registers([u'a'])return (var.get(u'a')+var.get(u'arguments').get(u'1'))
PyJsHoistedNonPyName.func_name = u'$'
var.put(u'$', PyJsHoistedNonPyName)