Iran - Afghanistan border (Islam qala-Taibad)
I took a shared taxi from the mashhad's main terminal to the border (only 4-5 $) then from the border you can walk 2km or take a shared taxi (0.5$).after that you need to go to the immigration office which is 10 minutes walking. On the Iranian side they checked my bags and stamped out, on Afghanistan side no questions were asked and in 1 minute I made it to Afghanistan.
From the border you can exchange money and get a shared taxi to Herat (only 5$,bus are cheaper)