I got a complete driver's side headlamp unit for my S90 last summer from an eBay seller for $80. It was in near-excellent condition and included the wiper motor assembly. Replacement was fussy but not complicated...I had to cut a small slit in the plastic bumper cover to get the wiper arm through before the lamp unit would come out.

Another alternative is to buy a package of that clear plastic headlamp protective sheeting and repair/seal your cracked lens. The stuff is about 2mm thick and once applied is pretty well as clear as glass. I put this on both headlamps as soon as I replaced the broken one.

If you are going to keep the damaged unit, you should seal it asap, as water gets inside and rusts the reflector surface.
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Bob: son's XC70, dtr's '94-940, my 81GL, 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.