No Thai agents can assist you with US visas. The most they could do is application preparation or appointment time slots. US consular is notorious for granting/ refusing visas. Their piece of mind is every Thai applicants will certainly not return home if granted a US visa so your wife has to prove otherwise.
Technically your visa has ended on the day your money dropped below the requirements. At CW office, agents can sort this out provided that you add it back up to the 800K before you go to immigration.
The prices are used to be around
*****
extra to the officers, plus the usual 1900 fee, and the agent himself for the service is around 3000-4000.
If your landlord could file it online, you can ask your landlord to do so when you are about to renew your yearly extension, or when registering your 90 day. Those are a few occasions immigration actually requests to see your newest tm.30
Have you marriage license authenticated by the Thai embassy, consulate there if possible. US embassy in Thailand does not legalize any American documents for you here.