A jet engine overhaul is far more involved than you are likely aware of. My company charges around 5 - 10 million for a CF6-80c2 overhaul.
Jet engines are broken down into modules: fan/fan frame, stage 1 LPT blade set, LPC booster/stator, HPC rotor/stator, CRF, combustor, LPT rotor/stator, TRF plus the shafts that tie the low pressure ends together which run straight down the center of the engine (mid shaft/fwd shaft - part of the LPC module). There are three gearboxes - inlet/transfer/accessory - and six main-line bearing sets. *LPT = low pressure turbine, LPC = low pressure compressor, HPC = high pressure compressor, HPT = high pressure turbine, CRF = compressor rear frame, TRF = turbine rear frame.
For an engine to be classified as "Overhauled" or heavy maintenance/full overhaul workscope, only the main modules need be completely disassembled, measured, repaired, and reassembled. Engine life is set by "cycles" and not hours so when a module is built each life-limited part (LLP) in the module must meet a minimum number of remaining cycles. Generally 3000 cycles is used as the basis. Some customers may only want their engine rebuilt with 2,000 cycles remaining because they don't want to replace an LLP. The lowest remaining time LLP will determine the engine cycles remaining.
While the overhaul costs are mind boggling, here is some trivia that makes me scratch my head every time I see the invoices: HPT stage 1 turbine blade set, qty 80 blades, cost: 1.04 million ($13,000 each). HPT rotating interstage seal, qty 1, cost: $1 million. HPT fwd outer seal, qty 1, cost: $1 million. The two HPT turbine disks have a combined cost of about 600,000. The thermal shield is $200,000. These prices relate only to the high pressure turbine module. There's still the fan, LPC, HPC and LPT to be addressed.
Rarely is an overhaul performed using all brand new parts so those new parts prices are not incorporated in every overhaul. However, when an engine is inducted for LLP expiration then all of the out-of-time disks, shafts, and seal will get replaced with parts that have remaining life cycles requested by the customer. I do recall rebuilding a few engines for an Arab king who specified that all brand new parts be used. He literally had money to burn.
This is a very vague description of some of what is involved with jet engine maintenance. It's very complex and expensive. I'm surprised that we can still buy airplane seats so cheaply with all of the associated expense tied to the flight.