Again project is in Planning stage and here we are using Estimating cost process which fall under Planning process group and Cost Management Knowledge Area, thus, here Budget Estimate can be used and Budget estimate uses range of - 10 percent to + 25 Percent from actual cost data, thus, keeping cost data upward by 10% for the difficulty, is not anything wrong here, as actual estimate can't be determined during planning stage or without going through executing stage entirely, again keeping such 10% extra can be considered as contingency reserve, that can be added with the project estimate or parametric estimate, this reserve can be used by project manager and he or she has authority to manage and control the same, further it can form cost baseline using project estimate and Contingency reserves, if correct historical data is used, then I must be comfortable with such estimate, because it has gone through known procedure of Parametric estimate and Budget Estimate,