Subject: Re: [their request]

Hi [CLIENT NAME],

Happy to help with that. Since [REQUEST] is outside the scope we agreed
([ORIGINAL SCOPE]), I'll write it up as a small change order:

  [REQUEST] — [$X], adds [N] days to the timeline.

Reply "approved" and I'll fold it right in. If you'd rather keep to
the original scope and budget, that's completely fine too — just let
me know which way you'd like to go.

Best,
[YOUR NAME]
