Most professionals charge $5–$10 per standard kitchen knife. Per-inch pricing ($1–$2/inch of blade) is also common. Expect to pay more for specialty blades like ceramic or Japanese knives.
Home cooks should sharpen every 6–12 months. If you cook daily, every 3–6 months is better. Use a honing steel between sharpenings to maintain the edge.
For most people, yes. Professionals use precision equipment (whetstone systems or belt grinders) and can match the original edge angle. DIY sharpening with a pull-through sharpener can damage the blade over time.