i have an artist daughter who was working for a law office in another state. the owner of the practice wanted a portrait of his two daughters, together, as a holiday gift for his wife. after establishing a ball park figure for the work, daughter put in countless hours, doing a photorealistic portrait in mixed media, and brought it to him for approval/purchase. he looked it over, pronounced it perfect, but too expensive. when she would not come down in her price, he had the nerve to ask if he could get a xerox of it for $25, instead. it remains in her portfolio as an example of her work, and a reminder of how fickle clients can be.
set a fair price. stick with it. do have the client purchase the fabric if you can, so they have an "investment" in the piece. get your contract in writing, if at all possible. no, you don't have to bring in "the law", but a visible contract is more binding than a verbal one. and know that the "workman is worthy of his wage". your artistry is worth it!