Flying from BKK to Luang Prabang, I imagine I get my visa right there at airport.Just going for 2 weeks.

You should get your visa on arrival just like from the friend ship bridge.

yes you get it ..... see http://www.laos-guide-999.com/Laos-border.html#airports

If you are from one of this countries as myself, you no need any visa ...

Lao Visa Exemption

Citizens of Japan, the Republic of Korea, Russia, Luxembourg, Switzerland, and some ASEAN member countries are exempted from Lao visa. The citizens of these countries (with valid passports) can enter Laos and stay for 15-30 days without a visa. For longer stay, a visa is required.

Yes you can, just did this last week, around US30-35, depending on your natioanlity.

Beware, carry US $ for that purpose, if you have baht, you pay a lot more. It pays changing your baht for the required amount in US$ at BKK before you leave. Dutch psport, 35 US$, 1500 BT. The difference buys you a meal in LP!