Upvote:5
It's a stunning country, but does present problems for some of us with stamps from there in our passport, especially trying to visit the US.... ;) But I digress...
For a while it was nearly impossible, but visas are indeed available for US Citizens, however, not on arrival. Now you can get a visa, but you must be part of an official organised tour.
For a full guide, have a read of Intrepid's guide on the matter.
Fees vary depending on your citizenship, how urgently you need it etc, but would suggest applying 60-90 days in advance, it can take time...