Start by developing a business plan - you can find books devoted to this. If you have written it properly - you should have an approximate starting cost, operating costs, your target consumer, expected revenues, etc.
It will be extremely tough to find investors for a service - venture capitalists usually fund new technology/products.
If you don't have the money, first consider asking friends/family, you can also apply for small-business loans. Try
Small Business Association for more info.