Not to slam the person that's been working on it, but.....

If you're hiring a mechanic, be somewhat selective about who they are. The right person, one that specializes in Volvos, will know how to narrow-down the problem BEFORE they start throwing a bunch of expensive parts at it. And they won't send you home in the car until they know it's right. Just for example, your problem could be low fuel pressure, a vacuum leak, or a slipped timing belt. These sort of things can be checked without buying a single part. Or if you want to make a SMALL investment in parts, try replacing the spark plugs with standard copper core plugs - under $10 for all 4.

If you post your approximate locale, maybe someone here would know a good mechanic in your area.