It depends on several factors like – the room size, the professionals you need to hire for different tasks, the cost related to taking the permission if you require plumbing, kitchen set up or not, etc. If it's a DIY project, then the cost will range from $5000 to $19,000 (as per HomeAdvisor). So, the thing is you need to plan according to your budget. You can easily restrict the cost to $5000, including permission costing. Taking permission requires something between $1000 to $1500.