A great article to give you an idea of what pays you back on a remodel is below.
I am wondering if you are asking what is the cost of finishing a basement or what is the return on your investment of finishing a basement. There are alot of variables to consider. Is the basement exposed (or partially exposed) are you adding a bathroom or other plumbing? Are you adding any special features, ie: a theater room, exercise room, etc. Plus are you handy and doing most of the work yourself, or hiring a professional. One word of advice: make sure you check with your municipality and get any and all necessary permits. And- do this prior to doing any of the work. Every municipality is different on what they allow a homeowner to do. Some require an electrician to do any electrical work, others allow the homeowner to pull the permit, and do the work, with the electrical inspector checking the work when it's done to make sure it is done to code.
As a veteran of many basement remodels, it is quite fun and rewarding. It gives the home more enjoyable living space, especially for those of us that are surviving many weeks of cold weather!
As with building a home, the price per square foot of finishing a basement will vary depending on type of finish, if you add a bathroom/fireplace, what condition your basement is currently in, etc.
If you are looking for some rough numbers to see if it is right for you at this time, a good rule of thumb is to estimate $35/sq ft for an average to start.
As a contractor, I review each homeowners goal and am able to give a bid with all allowances, etc. so you know what to expect up front. If a contractor is not willing to do that, I would recommend interviewing others.
If you have further questions, visit my website at http://www.essencebuilders.com and feel free to contact me for any other information.