Can I obtain a Non-O multi-entry visa in Savannakhet after my 90-day visa expires?

I have a hard time understanding your post, but I think there's two things you're discussing:

1. A one year, Non-O Multiple Entry visa based on support a Thai wife. You can get that at Savannakhet. There is *NO* proof of financial requirements for this visa. However, you MUST leave the country every 90 days. If used correctly, you can get about 15 months out of this visa.

2. An extension of stay based on marriage. You need to have 400K THB in a bank account for 3 months before the extension is approved. You can get an extension of stay at your local immigration office. You can stay in Thailand for the entire year, but you must do the 90 day reports.

Whether you get a 90 day single entry non-O and come into the country has nothing to do with you going to Savannakhet Lao and getting a new one.

You can certainly go to that consulate and get a year long, multi-entry Non-O visa from Savannakhet based on marriage to a thai with NO proof of funds at all.