import re
pattern = r"^.*?(?<!\d)(\d{3})(?!\d)"
s = ("\"Depart: NYC (etd 9/30), NJ (etd 10/4)\n"
"Arrive LAX\n"
"Rate: USD500, 700P\"\n")
m = re.search(pattern, s, re.DOTALL)
if m:
print (m.group(1))
aW1wb3J0IHJlCiAKcGF0dGVybiA9IHIiXi4qPyg/PCFcZCkoXGR7M30pKD8hXGQpIgogCnMgPSAoIlwiRGVwYXJ0OiBOWUMgKGV0ZCA5LzMwKSwgTkogKGV0ZCAxMC80KVxuIgoJIkFycml2ZSBMQVhcbiIKCSJSYXRlOiBVU0Q1MDAsIDcwMFBcIlxuIikKIAptID0gcmUuc2VhcmNoKHBhdHRlcm4sIHMsIHJlLkRPVEFMTCkKaWYgbToKCXByaW50IChtLmdyb3VwKDEpKQ==