In the past, I have used bus tickets to show "Onward Travel", The cheapest I found was Hat Yai to Penang. As you already know, you don't actually have to get on the bus you just have to show that you've purchased tickets to leave Thailand.
"The people here survive on about $1000 a month or less and it’s a different story for them" It's doable but it's not very comfortable. When I was teaching 6 years ago, I was earning 45,000 (about $1500 USD) and I found that was enough to pay rent and buy groceries but not enough for the 'extras' new cell phone, lost passport, travelling, etc.
I taught at a government school which the lowest of the low (income, quality of education, facilities, etc). Private schools pay more from what I understand. I believe a serious teacher at a private school earns in the neighborhood of 100,000/thb a month. I consider that pretty good, not great.
There are some places that offer "legal services", your partner may find employment through one of those agencies, I have no idea what the income would be.
Other that, SCUBA diver instructor.
As stated above most expats bring their job or income with them.
I am in a similar situation. I work remotely for a good company and I earn a pretty good salary. The company doesn't care where I live but they're not sending me to Thailand nor is it publicly trading. So I meet much of the requirements for SMART but it isn't applicable.
I have been here on Tourist visa for quite some time. You can do a Multiple Entry Tourist Visa which gets you 9 months. During that time you can figure out your next steps. In Thailand you will meet people who have connections, etc.