There are few things that will always get you within budget.
1, Proper staffing - At Kick-off, you should have REAL SENIOR Staff assigned to the project, A True senior guy should be able to outline the applicable systems choices in a heart beat, he will pick the best system with a complete work plan on how to execute, how to produce, etc.. Junior folks - they should just listen in a tight budget project (this is no time to teach)
2. You should teach your people how to use a database, how to reproduce and edit previous "Generic projects" to suit the new application.
3. Teach your folks what IS Relevant and what IS NOT Relevant on contract documents, and stick to the relevant part.
4. When push come to shove, you can write your specs with some parts as "delegated design", and only review and approve during shop drawing phase (sometimes it works so well, you could get away with murder).