Hi Joseph,
I know it sounds basic, but all of the incentives and contractual details really won't do what you want if you don't have a contractor who is experienced in that type of work, and who has a record of performance. That experience is what can save you $$ on the budget and insure a good job.
To find the right person it is so important to establish the relationship before trying to enforce terms.
It is best to find a contractor through referral, but at a minimum one who has a list of testimonials from clients for whom he did what you want him to do. Talk to his past clients...but also establish good communication with him. A contractor who has good relationships with clients and suppliers, will bring commitment and reliability to the table. You can't replace that with contractual terms. Though a good contract is important for both of you.
If you find a contractor with whom you can form a good relationship, you may find that you don't have to worry about enforcing contract terms so much. It's not a public works contract. A quote should work OK, and consider a penalty for going past the completion date, if you must. If you make it too complicated you could run a good contractor off or cause him/her to adjust prices up to cover contingencies.
It is important to keep it grounded and maintain the relationship. Good contracting is based on character as well as experience. Find both and you can relax and enjoy. Good luck!