The depth of a water well for drinking water will vary depending on how deep the waters aquifer is in your area.
Some wells only need to be drilled to 200 to 300 feet to reach the aquifer and supply adequate safe drinking water but then some places the aquifer may be as deep as 500 to 1,000 feet.
If we knew the location you're in we could give a more exact answer but expect to drill a minimum of 200 feet to get to drinking water but it can be as deep as 1,000 feet in some places.
Most water wells cost between $3,000.00 to $12,000.00 for the well drilling, casing and, well pump, tank and installation.