I know that Lao Airlines has a flight, but I am looking for a more cost-effective way of doing this trek (flight is 120 USD one-way). Time is a concern, and would like to do this as least expensively as possible (surprise-surprise!). Any ideas? Thanks in advance!
Well, assuming you don't want to fly, the quickest way by bus would be :
Siem Riep-Poipet-cross to Thailand-Bus from Aranyprathet to Nakhon Ratchasima (Khorat)-change bus for bus to Nong Khai-cross border to Vientiane.
If you were to leave at the crack of dawn you may be able to reach Nong Khai in a day, but more likely you'd end up doing an overnighter in Khorat.
Hope that helps