Which is the cheapest way to manage my body after death ...

Direct Cremation but if you don't mind your body going out of your family's control donating your body to science or a body farm for forensic anthropologist. It can be free.
- Came here to say this; cremation is the cheapest that leaves your family with an object; leaving your body to science can be zero-cost (costs paid by the institution of choice).
- I've signed up for donation for dissection. One slight caveat is that the institution - in my case a medical school - can decline to take your body if you've died of something infectious or if it's been too damaged, eg in a crash. If all goes well, they collect the body, and when they're finished with it they have it cremated. Family can have the ashes if they want. There's a nice memorial garden with the names of donors. It's all free... I mean, this is the medical school where Burke and Hare sold their murder victims, so they're quite grateful to get your corpse for nothing.
- Seconded on donating. It was free when I needed it for a family member and they sent a really lovely memorial letter. It listed all the things the donations went to like helping to restore sight in a veteran. You also still receive the cremated remains afterwards. Its a great option.

Die without an estate and tell your survivors not to claim your body. The government will take care of your final disposition.
- I could die with those glasses that have the nose and moustache attached. Nobody world recognise me.
- Depends on where you live. In Germany the government will of course take care of the burial of no one else does it, but parents or children are responsible for whatever burial cost is left after using the estate, even if they refused the inheritance.

I rather like the notions of composting or just being planted in the dirt with a bunch of trees. Not sure on the rules or costs though.
- Although by far the eco friendly option, natural (or direct) burials are still quite expensive, at around $2600. Most of this is related to the cost of the plot itself, and most of the savings come from using a cheaper/no casket.
  Direct cremation is generally cheaper, being $800 - $3000, with most options averaging around $2000.
  How Much Does A Green Burial Cost? - https://choicemutual.com/blog/green-burial-cost/
  What is the average cost of a cremation? - US Funerals Online - https://www.us-funerals.com/what-is-the-average-cost-of-a-cremation/

Get yourself taxidermied by the one and only Chuck Testa, and have your body posted up by a Walmart to scare the local community.

I mean in theory you can pickle yourself for like $200. If you're looking for option c
- Are your thinking in the bath tub or more like a human sized glass jar?

Just throw my body in the dumpster.
- Never thought of that. We segregate our waste here so there is a bin for compostables.

Have your corpse wrapped in a tarp and weighted down with concrete blocks from a construction site, and have it tossed in an abandoned quarry. That's probably about the cheapest way; should only cost about $10 for the tarp, and then gas money.
- I like that one, thanks. I could probably enlist an apprentice serial killer to help with that. Although I’m not sure how I’ll issue him with his certificate.

Don't? It won't be financially great for whoever has to deal with it, but it will cost you $0.

- I’m doing my post-life worrying in advance.
- If you have loved ones who will be financially worse off without you then this is important. Make it easy for them to grieve without worries about paying all the costs.
  even if nobody is finencially worse off without you taking care of this now saves them from preditors in the funeral industry. However this really one makes sense when you are old enough to know where life has setteled everyone - otherwise you might move and now your funeral is someplace where nobody rememberes you.