Whether Thai or Lao there seems always a price to pay there. Crossing with my gf (Lao) she is asked for money both ways by Lao immigration, normally gets away with less than asked for as she tells them she pays a lower amount at Savannakhet. And I also make sure my US$ are crispy, guy seemed rather disappointed the last time. They also had a new irritating arrival/departure card thing for me to fill out, never asked for the departure half on the return leg though.