when you get an extension ask immigration when you need do ur 90 days
Many immigrations will reset ur 90 days to the day ur extension is issued
As to the original question
come in on a visa exempt, apply for a non O visa ( 2,000 baht)
deposit ur money, after 2 months back to immigration and apply for ur 1 year extension ( 1,900 baht)
Via an agent anywhere from 25,000-50,000 , all depends on where you are with Pattaya the cheapest
Not hard at all,, either way