Let’s assume you have two level SFH with 3000 Square feet on the top two levels. Your basement is probably around 1500 square feet. If you were to finish this basement the way a builder would without upgrades this would cost about 25k to 28k. Price will very significantly when upgrading materials and adding features. Such as lighting, carpet, bathroom upgrades, a bar or a media room. You must have permits and the inspector will require licensed electricians and plumbers, also be mindful of fire block requirements before you begin. Hiring the right contractor can save you allot of headaches and time, check references and have a detailed contract. Also do not give to much of deposit, 20% to begin work is reasonable, progress payments are ok as long as they are talked about in advance and it’s a %based on how far the job has progressed. For example if the job is 75% done it would be ok to pay up to 50% of the contract amount.