Decks are less expensive than most other home additions. And because decks are so popular, they also make homes more marketable and valuable. Here's a look at what they cost. For basic designs using the least expensive lumber, you can expect to pay from about $6 to $8 per square foot of deck area. Even if you choose top-of-the-line redwood lumber or want a hot tub, material costs are still reasonable, anywhere from $20 to $35 per square foot.