Diyarbakir-Mardin is about 280-300 Km. might take 4-4.5 hrs. Busses are not expensive in Turkiye. From Diyarbakir to Silopi might take app. $30 one person/one way. I cant give you any price for taxis, you have to negatiate. Wont be less then $150-200 from Diyarbakir to Silopi.
Borders... I really dont know how the border is now a days. If you want to cross it, I am sure you will.
best of luck
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