@Peter *****
there are no 90 day extensions of stays from the immigration office on year-long, multi-entry Non-O visas. You are confusing terminology.
If you hold a year-long, mulit-entry Non-O visa you stamp out and back into the country every 90 days to get another 90 day admitted until stamp. It is NOT an extension it is a brand new entry on that visa. YOu do that for the validity of the visa itself.
The only extensions of stays you could get at the immigration office on that visa would be a 60 day visit family extension (which requires no financial proof) or a year long extension base on marriage which requires 400K baht banked for 2 months or 40K baht a month in imcone using a letter from your consulate.