I would budget around $20,000, but it's very difficult without seeing the property. It's also very hard to get contractors to come and give you bids when you don't own it yet.
Once you purchase a home, I would call PJ Rielly who is an honest contractor. PJ's number is 415-317-7371.
Your real estate professional should also be able to tell you how much the improvements should cost or at the very least give you some sort of idea. Your agent should also be able to give you some names and numbers of contractors and handyman's.