Motorbikes run about 150 baht/day for a 110cc motorbike and 150+ baht/day for a Honda Wave 125; supplied with helmets and a security chain. If you rent longer term, e.g., by the month, those rates can be as low as 2,400 to 2,700 baht per month, averaging 80-90 baht per day. Several dealers will agree to these rates. Currently a Honda PCX rents for 350-500 baht per day in the city centre. Monthly rates may lower the daily average.
Larger machines cost 700 baht/day for a V-twin chopper or larger sport-bike. Expect discounts when renting for a week, month, or longer.