Im creating a system to use donguri seeds to restore the previously highest level.
Low level restoration will be cheap.

You will not be able to restore your level if you are currently under level 5.
The cost to restore your level will grow rapidly if your previous level was really high and the gap is large.
The maximum it could cost to restore your level is 256 donguri.

Restoration cost estimates:
From level 5 to 6 will cost 0.00004117 donguri
From level 5 to 30 will cost 0.00164531 donguri
From level 5 to 100 will cost 0.03382381 donguri
From level 5 to 256 will cost 9.99888508 donguri
From level 30 to 40 will cost 0.00120643 donguri
From level 30 to 60 will cost 0.00543169 donguri
From level 5 to 345 will cost 252.10002136 donguri
From level 5 to 346 will cost 256.0 donguri
From level 5 to 1000 will cost 256.0 donguri