Look it up.....the concensus estimate of building the entire wall is 25 billion. The absolute least amount was 15 billion and the absolute highest was close to 50 billion.
https://www.congress.gov/congressional-record/2006/9/29/senate-section/article/s10608-2
...The bill will dramatically raise spending and increase welfare costs. The Congressional Budget Office and the Joint Committee on Taxation, JCT, estimate that this bill would increase direct spending by $16 billion over the 5 years and $48 billion over 10 years...