Deck Staining and Sealing Costs. Hiring a professional to clean, stain, and reseal an average size (approximately 250 square foot) deck costs $700 to $1,000. Depending on the size and layout of your deck, actual costs could be less than $500 or $1,500 and up. For sealing alone on a 250 square foot deck, expect to pay $300 to $400.