Non payment from Client

Myself Rohit , me and my wife run an architectural and interior design firm. One of our family members approached us for interior work. We visited their home and noted their requirements. We prepared designs and 3d drawings as per their demands. We gave them final estimate according to their specific requirements also mentioning our professional fees. Considering our family relations we had decided to way off the separate 3d design charges, but after the completion of all the design work from our side they told us that they were not interested to do the work as estimate was high. We had already given them designs so we asked them for the design charges which they refused to pay. After some discussions they said that they are ready to pay an amount but it's 1/4th of what we had asked for and they refuse to pay more saying that we didn't mention them that we would charge for design. Even the amount that we asked for is too less than the market rates. Our problem is that we had not made any contract as they were family and their point is that we didn't mention the charges before giving the design.Please guide me what can i do to get worth of my design.