Measure the area of the basement that you want to remodel.
Multiply the length times the width to obtain the total square footage of the area.
Multiply the square footage of the area by $25 for the low-end estimate. Multiply the same area by $50 to get a high-end estimate.
Draw a sketch of your basement on grid paper. Add in all of the rooms you will potentially remodel.
Label each room according to its usage. Calculate the square footage of the bathroom area separate from the rest of the basement.
Multiply the square footage of the bathroom by $75. Multiply the rest of the square footage by $25. Add the two together for a low-end cost. For a high-end cost, multiply the bathroom area by $150 and the rest of the basement by $50.
Add any special features you plan to include in the renovation such as specialty flooring, egress windows, a bar or fireplace. Calculate these items at cost, plus 10 percent for installation.