Creative Financing- is hard money the best option?

[Molly O Branson]

Hello! I'm under contract for my first multi-unit purchase (4 unit). The building needs a lot of work-- electrical, plumbing, roof, new kitchens, etc. I received a bid for $90k for the whole renovation (not including the cost of permits) and had a miiiinor panic attack. I'm comfortable covering $50k of this, but anything over isn't entirely doable. I'm wondering if getting a hard money loan for $50k and then paying it off through a cash out refi would be the best option here? Or rack up some credit card debt for a few months and pay the minimum payments... Some details below:

Purchase price: $438k with $13k credit 

Appraisal in it's current condition: $477k

Building across the street (same layout, slightly better condition) just went under contract for $575k

I'm very confident the property will be worth at least $500k once the renovation is complete-- just not sure how to get there! Any advice would be appreciated!