Yeah ED visa is very expensive, that why the best option is marriage extension or retirement. I am marry and I pay only 1900 bath every year at immigration
You have to marry with Thai lady if you want to stay long time in Thailand. You can't apply for an extension based upon on retirement as you are less than 50. Student visa could be an option for one year living here
I would always avoid divorce in Thailand, especially because am still too young to get an extension from retirement. You don't have too much choice to stay here long term, unless you are married to a thai or retired