Right, on your arrival to any airports or Checkpoints in Cambodia, you just tell to the officers at the airport that “I would like to have a Business Visa and I am happy to pay more” then they will give you a Business Visa. Please imagine that, paying more to get a Business Visa, you could do a self-drive, having more privacy, and saving cost of hiring a driver of $30.00/day and paying less to get the Tourist Visa which you could not do a self-drive, travelling without privacy, and paying extra to hire a driver at $30.00 per day. Which one is economical?
Even though the Business Visa costs you a $100.00, it would also cheaper than hiring a driver. But the Business Visa would cost you around $45.00 to $55.00. Just ask them how much for the business visa. Do not be so rush when you are checking in to the airport, just pay sometimes to understand the psychology and the flexibility of the officers there and do the negotiation with them in order to get the Business Visa.