It is hard to say because the main costs are trying to not get defrauded, complying with money laundering laws and accounting laws and trying to not get hacked.<p>If you let people deposit money by bank transfer then fraudsters will constantly do things like get gullible people to send a deposit to buy a second-hand car to the exchange bank account, turn the money into cryptocurrency and move it before the banks get a request to return the money.<p>A typical business bank account will soon get closed by the bank.<p>There are many stories from the early days. In the early 2010's there was a money transfer service called Dwolla. It was run by some young men who did not like how banks work and thought they could do better.<p>Dwolla promised "no chargebacks". They were used by a long-dead exchange called Tradehill. It ended in bankrupcy, lawsuits and fines.<p>Making a profit of a couple of percent on each transaction is easily turned into an overall loss when banks yoink money back out of your bank account.<p>The early exchanges had backend code written by wildly impetuous people and really basic security problems like SQL injection.<p>Leaking all your customers account details through one bug in back in code could get you a big fine.<p>People selling crypto for cash find that fraudsters will turn up in person with large amounts of high-quality counterfeit bills.<p>There is the risk of being kidnapped because you can be beaten until you type on your laptop and transfer cryptocurrency.<p>One screwup can sink an exchange. There was the Bitstamp hack in 2015.<p>Bitstamp said "we are super secure, only a few laptops can access the back end".<p>They had Skype and Microsoft office on the laptops! One of the staff opened a Microsoft Office document with macros from a phisher on Skype. That is literally running malicious software. With invisible control of the laptop, the criminals rapidly stole a fortune.<p>Consider spending three weeks reading the bitcointalk forums right from the start in 2009 to see what a wild-west you are considering getting in to.