You can apply for a visa through the mail. The directions say to allow 6-8 weeks, but we actually got our passport back within 3 weeks. YOu can send a priority US mail envelope with the visa applicaiton so that your passport can be mailed back via a faster method (but not overnight). At this point in time for a tourist visa you do not need a letter/invitation. The form is one page and takes maybe 10 minutes to fill out. I can't recall the visa application cost, but I think it was around $30 USD.