That's a tricky comparison because they solve different problems in different ways.

**FCMP++ fee reduction**: Probably 60-80% smaller than current ring sigs due to proof compression and better decoy efficiency.

**Mimblewimble**: Would likely be even cheaper - no ring signatures at all, just cut-through eliminating most transaction data. MW transactions are tiny.

**But here's the catch**: Mimblewimble on Monero would break everything that makes XMR actually private. MW has no sender privacy (you can trace transaction graphs) and timing correlation attacks are trivial.

You'd get cheaper fees but lose the core privacy guarantees that make Monero worth using in the first place.

FCMP++ costs more than MW but actually delivers on the "private money" promise. MW would just be expensive theater - cheaper to run but worthless for anyone who needs real privacy.

It's like asking if a paper lock is cheaper than a steel one. Sure, but what's the point?