Hi Lotus,
If it’s successful it can save you a substantial amount vs buying a completely new mattress although your mattress won’t have a “finished” look to it.
If it’s not successful of course then it can cost the amount of the layers you purchase (although in some cases you may be able to re-use these either as part of a component mattress or as a topper on a new mattress).
There’s more about mattress surgery in post #2 here and the links it includes.
Phoenix