This eliminates you paying an unknown amount when all is said and done. The cost of hiring an interior designer varies greatly. Most charge per hour, with the current market rate between $50 and $200 per hour.You would pay this in addition to the cost of furniture, accessories, artwork, etc. Some interior designers charge their clients by marking up the decor they choose.his eliminates you paying an unknown amount when all is said and done. The cost of hiring an interior designer varies greatly. Most charge per hour, with the current market rate between $50 and $200 per hour.