Motorcycle Rental

If you are talking about something like a Honda Wave then the places that rent are too many to list - just about any 'falang' bar to start with, plus many, many Thai places advertised as you travel around. The price varies considerably (down) with the longer that you rent for. From memory you can rent 1 for about 150 a day but you probably need to be careful on what the 'insurance cover' is like. In many places it is third party only & you will pay (sometimes not cheaply) for any damage done to the bike.
If you are looking for anything on the large side then the only place I can think of is Lek Car rentals. The one thing about Lek is that you can be sure their insurance is first class.

Although many travel around Udon helmet-less you will undoubtedly end up getting stopped & fined by the police if you do.
What you are charged for any damages depends on what is written on the agreement that you sign to rent the cycle. Some charge over & above the actual cost of damage as they will claim that you have prevented them from re-renting out the bike until it can be repaired. It is also important that you fully check the bike over before hiring & ensure that if there are any marks they are fully recorded on the hire documentation..

BobHelm wrote:Although many travel around Udon helmet-less you will undoubtedly end up getting stopped & fined by the police if you do....

...... it should also be remembered that in many hospitals around the world motorcyclists who don’t wear helmets are more simply referred to as donors