Driving a car in Bangkok and Thailand is not for the faint of heart. The only place I suggest to ride a scooter is around the village, upcountry or wherever. If you plan only to ride a side soi and park at transportation, that may work, but be prepared for theft.

I know a young man that spent his savings, bought a bike and thought he would be a courier in town. He had several wrecks and quite scrapped up. Maybe he did not have the skills, but that was his experience.

I would simply pay the point to get around town by available means. You will literally be taking your life into your own hands in metro traffic. Be careful.

If you are leaving every month then you probably only have a VOA or (Visa on Arrival) which is automatically granted when entering the country from most countries and it is only for one month.

It's not a VOA (visa on a arrival) it's a visa exempt stamp. Therefore you have no visa. Please make sure you are posting correct information.

To the OP, I suggest you rent first and make sure you will be comfortable driving a bike in BKK. Really you might find that you don't need a bike in BKK, public transport is very good and motorbike taxis can be found everywhere.

Most of the posts tell you what you need to buy a bike. What you need to RIDE one is to be crazy brave, even off the main roads. Good luck !!!!!!

if you dont know Bangkok and if you will stay here for short time, just use public transport and motorbike taxi.

Roads are congested in Bangkok and pretty complicated besides, you need some experience before and you need to build up some skills so if you will stay short, just dont get tired and sweat!

On finance:

Valid passport and visa, Thai national guarantor, 25% deposit (less for a Thai national)

Cash:

You will need your passport to change ownership papers. Can be done at local MOT. The seller may only give you the paperwork pre signed, with a copy of their ID card. The MOT should accept that, and May even let you forge their signature as long as have the green book and a copy of their ID. (Personal experience)

Don't recommend buying a bike without a green book. Some horror stories about that. Also, mechanics in Thailand are awful. Recommend buy a new or late model bike.

What makes you think mechanics in Thailand are awful? I have used them for the last eight years for my motorbike, and cars. Every single time I have been pleased with both the service and the cost, and their has never been any comebacks. How many buses in Bangkok are over 50 or 60 years old? How many times do you see these old buses broken down at the side of the road? Does that not say anything about Thailands mechanics?