I park up at the bridge, buy a bus ticket at the kiosk a bit further on, 50bht.p.p. They do squeeze you on, but I have never had a problem.
Bus is usually ever half hour, though I have a feeling the first one is 9.30am, because I waited nearly an hour. Then I get off the other side of the bridge, do the Laos visa thing and get a taxi/tuk-tuk from there to the Consulate, 100bht.p.p..