@David *******
the visa to enter Laos is $40 USD for most countries. If you pay in baht you are overcharged on the exchange rate.
One "potential" trap is they ask how long you are staying in Laos. I suggest you give some amount of time in days. That way you avoid any phony scams about fees for short term visitors. I even ran into that at a remote Cambodian crossing.
Oh, and the Laos border collects 100 baht from Thais leaving to return home. So if a Thai companion accompanies you expect that.