The number of pressurizations is one factor. Something like 10,000
(that would be 10,000 pressurizations, not hours) is getting up there.
The other item is engine rebuilds are horrendously expensive and can
swamp the cost of purchase. Don't believe Cessna's figures on per hour
running either. They are way optimistic.

Having said all that, there are some very useful, well used business
jets out there.

My advice would be to get an expert. in CESSNA CITATIONS. Probably a
Citation mechanic, and pay him to help you decide which one.