It is very easy to get a Turkmen transit visa in Mashhad these days. Vali, from Vali's non-smoking Homestay in Mashhad can arrange the visa without any hassles. For 5 euro's he takes on the mighty Turkmen bureaucracy. Here is how it works. Contact Vali in advance (allow one week at least)and tell him you want to apply for a Turkmen transit visa. He will ask for a copy of the first page of your passport and a copy of the Uzbek visa (scan it and mail it to him).
With that he can start the application process so that when you arrive the visa is basically waiting for you at the consulate. You don't need to think about entry and exit dates or points when you start the process. Once you arrive, Vali will go with you to the Turkmen consulate, where you will submit one passport photo, one copy of your passport and Uzbek visa page (Vali can print out the copies you sent to him earlier) and you need to fill out an application form (you can do that at your leisure at Vali's homestay as he has a bunch of them). Now it will be time to fill out the entry dates and exit dates and points (you can put whatever entry date you want, so if you still want to travel around Iran for a month, you can simply ask to enter Turkminstan in a month time). Once at the consulate, Vali will handle everything and most likely you will never see the consular official who gives you the visa. It took me all of half an hour to get my visa this way, once in Mashhad. With a bigger group it will take longer, but you won't be much longer than me at the consulate. Vali submits it in the morning, this is where you will be required to be present, in case there are any questions, and 3 or 4 hours later he picks up the passports with the visa. Transit visa costs 55$ for most European nationalities, 85$ for British citizens, and you need to pay in dollars! Also be aware there are only certain days that the Turkmen consulate handles application forms and hands out visa's for tourists (I think it is Saturday/Tuesday and Wednesday).
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