Dave is right, at 140k, there would be an underlying reason for the Head Gasket to blow, they will normally last at least 200k. With that in mind, as Dave stated, the most probable cause is an overheat. The worst case scenario it a head warped beyond repair. Just milling the surface may not correct the damage fully, the cam bearing cradle may be out of alignment and need to be rebored. The warp may be bad enough that the amount shaved off the head to flatten it may throw the head height out of spec and you could end up with an interference engine and not enough aluminum in the head to properly dissipate the heat, thereby warping it again. A reputable machine shop familiar with Volvo red blocks will know this and check everything out; others need to be told, but you don't want them doing the work.

A used head (there are plenty out there) should run about $300. Labor and extra parts will easily tack on another $600-$800 minimum. A used head should be freshened with, at least, new valve seals and valve lifter bumpers, these should come in a good head gasket set.

You can do this yourself if you are familiar with a wrench. Get all the parts together and it will take you a weekend, cost less than $1000 (maybe less than $600) and you can impress your wife and buddies. Spend what you saved on beer & pizza. The hardest part will be wriggling around under the car to disconnect the turbo & exhaust, use PLENTY of PBBlaster beforehand on all turbo, exhaust & exhaust manifold bolts/nuts.

Expect to replace all gaskets from the head as well as the water pump gaskets, new thermostat, timing belt & tensioner, and while you are at it (with everything off the car) clean the throttle body, IACV, and breather box. It will never be easier to get to these items.

'94 945T (daughter co-opted it for college, used to be mine)
'99 S80 (mom-in-law's)
'88 240DL (leadfoot son's)
'84 242Ti (commuter)
'89 560SL (wifemobile)
'88 300TE (for sale)
'68 GT500KR (under restoration)
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Bob K