If you have a Thai bank account and deposit the required 800K baht, you can also apply for a Non-O visa in-country with 15-21 days left on your stamp. These are the general requirements for a Non-O visa in Chiang Mai. I suggest you visit the immigration office in Chiang Rai to obtain a handout of their specific requirements.
You can only apply for a one-year Non-OA visa through the Thai embassy in your country of passport or country of registered permanent residence at the time of application.
If you are able or willing to transfer the required 65,000 baht for twelve consecutive months, you can, as you probably know, switch to the income method in order to free up the funds in your account.
The announced processing time is up to 10 working days, but many applicants receive their visas within 2-3 days. It's recommended to apply about 6 weeks prior to your intended travel date.
Formally, an exit ticket is required for all tourist entries. Certain embassies require documentation of at least two entry and two exit tickets before issuing an METV. The requirement is generally applied more strictly in connection with visa exemptions than with tourist visas. The final decision rests anyway with the airline and immigration.
You don’t need to prove or upload any tickets for a Non O visa, but you’ll just need to give a trip with flight itinerary for the application. When it’s issued you’ll have three months to enter anyway regardless of any dates.
The single entry gives you 60 days upon entry within three months. The multiple entries gives you 60 days each time you enter within 6 months. Both from the date of issue.