Commerces — shopping, and the market exchange

I can shop for food, ask the price, ask for what I want politely, and handle a simple market exchange on either side of the stall, and I know how to match 5 shops to what they sell; say where I shop; ask Combien ça coûte ? / Je voudrais ___, s'il vous plaît; assign each line of a market dialogue to le marchand or le client, put the exchange in order, and produce Je voudrais…, Ça fait combien ?, Et avec ceci ?