Most people are not very good at sticking up for themselves so I commend you on thinking about getting a negotiator. I agree about the union. If you don't like one, perhaps try another - negotiations are exactly what they are there for. Going wages will vary depending on region but are often higher than you think, especially for people who have been in the job a long while. Unions will often have some idea of going wages. They will also be able to help deal with that issue of not seeing the raise in the pay packet! :-?
These are just my experiences - but I think if you feel you have worth, and can be convincing, you will get more money, MUCH more money. Going into your own negotiation involves some gumption. This is what I usually advise: Make a list of your skills and attributes that make you a valuable employee. If you think you are worth $30/hr, then ask for $39/hr and when they balk, tell them why you are worth it - and mean it. When they continue to balk, tell them again why you are worth it (assertiveness technique #1, the broken record) and why their business will be better with you (what they have to gain). If they make a low ball offer, counter with a reason why you are essential to their business. Be pleasant, always.