I've never been charged by my agent or LL to do the tm30 and I leave thailand every 1-2 months. I don't really know if they actually do it every time as I never asked for the receipt.
So far, I haven't stayed more than 90 days so haven't needed the tm30 for any immigration purposes.
Your LL sounds like they're charging you for the inconvenience of renting out to foreigners. I honestly would move as soon as my lease is up and look for someone nicer
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