Not really all that difficult if you have the proper tools. Can't see why anyone would own a concrete saw unless they were in the business so you would have to rent. A small excavator rented would also save you from digging the hole by hand.
If you have a good concrete saw cutting is messy but not all that difficult, especially if the concrete basement is blocks instead of poured. And with poured it depends on how much rebar is in the wall.
While I said it's not all that hard, that is true. But it would be much easier if you had seen it done. Perhaps YouTube would have a video. Building the egress hole outside I thunk is best done with stackable stone. Plan for getting rid of the water that will enter the hole. Another concern, depending on the width of the window you have to plan for header. Any wall that supports a roof is super important. An end wall generally doesn't support as much as a sidewall.
Perhaps it's just easier to hire it done. Any contractor should be able to give you some references, if not, beware.