Yes, TPs are very expensive.
New TBM700/850 is about $3M.
A brand new big piston twin... are any made today?? A new Seneca is still being made, just about, which costs a small fraction of the TBM cost. Same for a couple of other piston twins in production.
However, the direct operating cost, excluding depreciation, is much closer. A piston twin like a 421 (somewhat comparable to a TBM in payload and range) costs a comparable amount in fuel and IFR route charges and landing/handling costs to a TBM, but the TBM gets there in less time.
Turbines are unfortunately an order of magnitude step in purchase costs...
A halfway house is a Jetprop type conversion. You can buy say a 2002 JP for $1M which is only a "bit" above a new piston twin. But you don't get the payload or a range of a 421 that way - nowhere near.