Just checked two examples that I've done recently without getting visas in advance: Turkey and Indonesia.

For Turkey, it admits that you can get the visa on arrival but tends to suggest not doing this. Visa on arrival is $20 versus $69 service fee plus $60 visa fee for going through Visa Centralwith standard service, plus an additional $49 rush surcharge.

For Indonesia, it says that an advanced visa is required and doesn't mention visa on arrival. I guess I shouldn't have been allowed to visit Bali according to Visa Central and SQ should not have let me on the plane. IIRC I paid $25-30 for the visa on arrival, versus $69 service fee and $45 visa fee, plus $49 for rush service. Doing the visa in advance requires submission of your bank statement and a letter from your employer.