Mr Alexander, whose seat is under threat, received the majority of the cash boost via two donations totalling £50,000 from Inverness businessman Alan Savage.
Mr Savage, the former chairman of Inverness Caledonian Thistle, is the head of Orion Engineering Services and was also part of Better Together.
He was also confirmed to have donated money to the No campaign.
The House of Commons register of financial interests shows he gave Mr Alexander £25,000 on two separate occasions last month.
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