It's the price of living in Thailand, if you don't like it go somewhere else, but as pointed out most countries levy some sort of charge on long stay foreigners.
However, if you consider the cost of 1 year marriage extension (Bht1,900) and add a multi-reentry permit (Bht3,800) the total (Bht5,700) is similar to the cost of a multi entry non-O marriage visa from Savannakhet (Bht5,000).