Unless you know the price, else you'll not get cheapest price.

Know what you want to buy, shortlist them, then compare the pricing offline and online. I would say there is not one shop that would have everything cheapest. If you have big item purchase like fridge, best to start from there, nego until cheapest u feel comfortable with then slowly add items and nego further.

Buying all from one shop wont be cheapest but would be more convenient to accept delivery in one go.