You'd like to ask your customer straight out - how much money have you got to spend? It's not perhaps the most tactful or advisable question and the answer is one that the customer would be pretty foolish to reveal. They know that you'd tailor your product or service around that declared budget, even if you knew that the real cost would be considerably lower. Good for you perhaps but a nightmare scenario for the client, harbouring resentment and a bad reputation for your business. You'd definitely not be offering value for money and will soon be found out.