Prepping a house costs anywhere from $0.50 to $2.50 per square foot. This is almost always included in the total project price. However, the DIYer might negotiate some discounts for completing this work on their own. Be warned, proper prep is key to the quality and durability of the finish. If you do this work yourself, the contractor might no guarantee to finished product.

The Ceiling. For ceilings, flat is recommended, except semigloss or satin should be used in bathrooms with showers/tubs. Some customers opt to go with a different finish for ceilings in general, to create a specific design look, i.e. high gloss ceilings on dining room tray ceiling to make a statement, or eggshell ceilings throughout to look modern and make a statement. 
While some professional painters will charge a flat fee for a painting project, most charge an hourly rate—about $25 to $100 per hour on average. Most painters will charge more for last-minute jobs (think 48 hours' notice or less), travel costs (if you live far away, the painter may want extra money for gas), or intensive prep work (e.g., removing mold or stains before painting). Also, depending on the painter, the rate may or may not include the cost of paint materials such as paint, primer, and supplies.
You might pay an additional $1 to $5 per square foot for optional repairs and updates. Consider having your molding, trim and baseboards checked while you have a professional in your home. This might be a good time to upgrade or repair any cracks, warps or other issues. Pros can usually touch up or replace these items for an affordable rate, and they may even package such fixups with your project.
Homeowners report that painting a home’s exterior costs an average of $2,923 with a typical range between $1,734 and $4,119. The average price per square foot ranges from $0.50 to $3.50 depending on your location, condition of your exterior and accessibility. Stucco and brick cost an average of $1 per square foot more than vinyl or wood. The average 2,500 square feet home costs an average of $4,000, though it can range from $1,250 to $8,750.
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