Basement renovation costs can vary widely, depending on the size of the room and what you plan to do with it. And of course, its present state of repair can also affect the cost. As a general rule, if you’re planning to renovate and refinish the entire basement, reckon on spending between $22,000 and $46,000, which equates to between $32 and $47 per square foot. However, you may need to spend up to about $58,000 for a large basement with a bathroom and several rooms. The cost to just add drywall to your basement will cost somewhere between $1,200 and $4,000 while insulating existing basement walls costs anything up to about $4,000. Adding or modifying the plumbing or electrical system are all potential costs too, and having a firm budget is a must. The good news is that your home will certainly be worth more.