Mostly in stock is 150cc as more people going for 150cc instead of 125cc. Most likely the dealer is not going to order 125cc for stock. Or another option is the Honda scoopy 110cc.
If you are only staying short term, why do want to have a Thai bank account? Paying an agent for an account to use on a short visit, will cost you at least 5000b or more for the account.
What visa are you having now? Tourist visa? If you have a non B or O visa, no additional charge to open an account.
If you are on tourist visa, they are selling you an insurance in order to process a bank account for you. If you really need a Thai bank account then just get the insurance that the bank provide. Bank will not scam your money as there is paper work involved in any money transaction.