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#11
Looking around eBay and other parts suppliers the going rate for a refurbished Dell OEM Inspiron 15 (7548) Motherboard seems to be around $250. You could save the $150 for labor by doing it yourself but, as the repair shop said, there's no guarantee it would work. Anyway, used working examples can be found on eBay in the $400-$600 range.
No, you're probably right. Best to put the money towards a replacement.