Automatically pull in data from 1 spreadsheet to another spreadsheet within the same workbook

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I have 2 spreadsheets, one is called "cost data" and one is called "approved budgets" and both change on a monthly basis. How do I automatically pull data in from cost data into approved budgets when the data changes consistently? For example, there is a column called 'weeks left until depletion' in both the "approved budgets" sheet and the 'cost data' sheet. A new line of data is inputted every week, so how do I write a formula where the "approved budget" sheet automatically pulls from the cost data sheet vs. me having to change it manually every week? Currently the formula for the weeks left until depletion column is ='1. Cost Data'!G67, and every week that the data changes, I manually change the formula to G68, G69, etc. I want to set up a formula so that when I change the data in the cost data sheet, the data in the approved budget sheet will change too.

I can't post the spreadsheet in this post, but I am happy to email it to anyone that can help!