I wouldn’t recommend showing them a bank statement that doesn’t have at least 20,000 baht in it , they will deny your visa. Vientiane has started enforcing policies as of late.
There are no “walk ins” anymore at Vientiane. There are buses from Udon Thani, but you need to have a Laos visa already before they will allow you on. If you don’t have a Laos Visa, take a bus to Nong Khai, cross the bridge and then another bus to Vientiane.