Consult with your faculty research mentor about your budget BEFORE you submit an application for funding. Do your research about costs so that your estimates are as accurate as possible -- there are multiple online resources that can help with this. For example:
If you are estimating room and board for a research trip, there are government websites that provide estimates for cities within the US as well as overseas. However, keep in mind that these are estimates for government employees traveling for business purposes, and the cost of student research travel should be significantly less.
If you are estimating the cost of travel by car, the IRS lists standard mileage rates. Note that the business rate is for employees traveling for business purposes, and undergraduates traveling for research purposes should estimate significantly less per mile (the "medical moving" rate would be a reasonable estimate).
If you are applying for a full-time Leave Term Grant for on campus research, apply for the full Leave Term Grant amount. You do not need to submit an itemized budget.