Help me estimate the rehab cost on this 4-plex!

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Pictures can be found HERE... Listed for 80k.

It's a 4-plex. 5bd, 4 bath. 3000 sq ft located in Duluth MN. This has been on the market for over 6 months and started out at 150k asking price. So seller is obviously looking to sell since they have come down in price by more than half.

My problem is that I don't have any idea how much it would cost to get this property up to c class rental unit standards. 10k? 20k?