Tourist visa only lasts for 60 days and you can extend it for another 30, then you get to 90 days maximum. After this time you do have to leave the country and re-enter again. The tourist visa is the one you get from your own country. The visa stamp on arrival only gives you 30 days. Price: 2,000 THB for visa and 1,900 THB for the 30 day extension.
You could get an education visa for either Thai Language or Muay Thai and study this part time, while you do your online trading. This visa lasts for 6 months to a year, and you can renew for another year to continue the studies (Depending on the school). Less than 5,000 THB. Does not include cost of tuition.
You can get a job in Thailand. Or you can start your own business here. This is more expensive for you to maintain over the long term -- but if the business is viable then that is not a problem. To start your own business, look to spend about 60,000 THB or 100,000 THB to both start your business and get your visa and work permit.
The Elite Visa is another option, which ranges in price from 600,000 THB to 2,000,000 THB for between 5 years and 20 years.
If you're over 50, then this one is potentially for you. You do have to keep some money in the bank or have a minimum standard of income. Price for visa is 1,900 THB and you can spend about 20,000 THB for a good agent that will help you with everything quickly.
Finally, you could be fortunate to find a Thai wife and get married and live in Thailand. You need to have some money in the bank also and keep renewing your visa each year.
There are other miscellaneous visas such as the Smart Visa and the 10 year retirement visa but those are more for investors and require bigger financial outlays.
What do you think most applies to you?