In Dec 2006 I entered Laos thru Nakhon Phanom / Thakhek on my Cambo registered DRZ after being refused entry at Nong Khai
Laos 30 visa, 7 day bike permit, 20 day bike insurance, were all issued on arrival at Thakhek.
Bike permit and insurance cost around Bt450
In Vientiane I went to the customs headquarters, 3rd floor and extended the bike permit for another two weeks to equal the insurance duration, no cost.
Assuming the bike is Thai registered go to your local registry and get a ITP for B55 for 6 months . Photocopy your passport, Green book, and just drive in (after doing the Thai export formalities). They will stamp your ITP , check the Thai export paper and send you on your merry way.
ITP = International Transport Permit. These subjects are all in previous posts.