It cost more to drive a motorcycle then a similarly prices car due to many factors Yes, accessories are a big part of that.
Helmet - $150 to $300 for a good DOT and SNELL Helmet
Gloves - $50 for a good pair for hand protection
Riding Boots - $150 and up for a thick pair of leather boots to keep you feet safe
Riding Jacket - $200 and up for a good riding jacket with armor for you back/shoulders, ect.
But maintenance on a bike is very expensive compared to a Car.
Car oil change at a shop - $30.00 - Bike oil change at a shop - $90.00
Car tires 30,000 mile ratings - $300.00 for 4 - Bike Tires $150 a piece for 5,000 miles.
And aftermarket parts for a bike are also sky high, like mufflers are over $300.00 for a good one.
If you get a smaller bike with good mileage and go easy on aftermarket stuff, it will be cheaper then a car. But tires are a big part as the super sticky rubber in motorcycle tires runs down after around 5,000 miles and the tires are not cheap to replace if you have the shop do it. If you do get a bike over a car, do no DO NOT Skinch on safety equipment that can save your life. A good new helmet, a good jacket, and a good set of boots are key especially if you are a new rider. If you live in hot weather climate like me get a jacket with good ventilation.
Last thing to consider, rain, snow, ice, and other drivers. Riding a bike in rain SUCKS, and if it is cold rain that is even worse. Ice is super bad for bikes, and the worst thing is stupid car drivers not paying attention. Just today I nearly got run over at a stop light. An old dude in a Nissan Hard Body Truck didn't seem me stopped at the light and slammed on his breaks and swerved into the lane next to me. Thank god their wasn't anybody else in the lane next to me or I would probably got rear ended sitting at a stop light. I didn't even seem him coming up until I heard the tires lock up and saw his headlights 3 feet away from my legs! So riding is very dangerous and I would not recommended it as a sole means of transportation.