@Ali *******
after lodging your application it may take 3 days before you can collect your passport from the embassy so don't book any airline tickets until you have you passport. Today's prices for next week from Udon thai to Bangkok DMK is only about 1500b and to BKK about 1800b. You can get the international bus from the bus station in Vientiane to Udon Thani. The bus stops at both of the borders for passengers.