New derailleur? I've never knew anyone who needed a new derailleur going from a 5 to a 7 speed using friction or index. Also I've known plenty of people who took there vintage bikes into shops and and had their freewheels replaced from 5 or 6 to 7's and was done cheaply with just the cost of a freewheel, and redishing the wheel if needed. Shimano freewheels as well as others are also cheap to buy.

Speaking of letting others not discourage you, what the hell was SEAcyclist100 doing if not trying to discourage you?