Generally US citizens or those traveling with US passport must be in tour. You should get a visa first and no guide can get you a visa unless you a tour with an official agency. The rules are very clear about American citizens, no agency risks giving you a guide only. Nobody likes to be in trouble for supporting American tourists by evading the law.
It doesn’t need to be expensive package tours which are all inclusive. ITS can offer budget tours with more freedom for Americans but there must be guide with you all the time and your accommodations must be booked. Using some public and private transport, we can cut down on expenses. The range of hotels used can be very different. Contact Iran Travel service for our best offers.