What is the highest service ceiling for turboprop airplane like a Cessna 425?
The PA-46-500TP Malibu Meridian can climb to FL300 and you may be able to find a high time one for under a million. 

Socata TBM has a quoted ceiling of 31,000 ft and you may be able to find an older TBM 700 high time airframe for in and around a million. 

In the multi-engine category:

A PA-42 Cheyenne will put you up to just under 36,000 ft and can be had used for under a million.

A Beech King Air C-90 will get you up to 30,000 feet and can be found used on the lower end of the price spectrum.