If you don't know what your doing, it is almost always cheaper to have it done right the first time rather than have someone else undo and redo what you tried to do.
Sign in a machine shop:
"Our rate is tripled if you attempted the work and failed."
Use a reputable contractor for repair and maintenance work, with references. Seldom is Craigslist the best place for these. It would really suck to wake up knee deep in water(or worse) because you wanted to save $50 on a thru-hull replacement.