You may try the Thai Embassy in Savannaket for a new TR visa, if you had only one TR plus extension yet. Make sure, you meet all requirements and probably it would be better to stay in Laos for a couple of days before going to the Embassy.
The SIM always comes with a small load. You can choose/ change the package as you want at any phone shop or Tops market. 7/eleven and AIS got divorced many years ago.