Small random-orbit or pad sanders make this job go faster. (Wallis first covers these boundaries with Synkoloid patching compound so no edge is visible after sanding.) As shown, you want to make sure that there is a feathered, smooth transition from exposed wood to old paint. For areas that might get close scrutiny, you can follow up with a 100- or 120-grit rubdown to erase any scratches.
The cost to paint a room will vary based on the size of the room, the type of paint you select, any ceiling or trim work needed, and any repairs needed. If no repairs or other additional work is needed, painting a room with contractor-grade paint could range from $1 to $2 per square foot, including materials. Selecting a luxury paint (some cost more than $100 per gallon) will certainly increase your house painting costs. Here are some additional examples of average house painting costs, per room: Home Painters