How do I avoid writing an unrealistic budget (either too low or too high)?
Ask for the money you need to do the work, first being sure that you are not being overly ambitious. As suggested above for reeling in an overly ambitious project, figure out the costs for a typical experiment, figure out how many experiments you can do in a year, and multiply the numbers through. Don’t try to do your work on a shoestring, but do not pad the budget either. Reviewers are very good at detecting padding. (They probably tried it themselves at some time.) Talk to experienced investigators who know what is a reasonable total budget to request from the grant maker to whom you are applying, if this information is not explicitly stated.