Every property is unique and you can somewhat calculate capex in todays dollars. 

A lot of what I've been seeing lately in the lower price ranges isn't really worth the bid for the areas I understand - I'm seeing MLS deals that are a better option.  

Listing it high with the plan to go lower in negotiation can work, but can also put you out of buyers' range.  

For residential investment properties most banks lend 70% LTV, and you can typically get the 15-30 year range, along with market interest rates (compared to hard money, which charge points and higher rates).

How should we determine the ARV of this unique home?

They said they charge interest rates ranging from 7-14%.

Now my loan broker is saying that he can’t find an appraiser that will appraise the property because it’s unique in the sense that it’s 3 SFRs rather than a traditional 3 unit building.

Depending on lender plan on DSCR 1.25%Plan on 65% LTV- and rates in the low 8% range right now- if you meet all those guidelines they are super easy to get approved

I'm looking for SFHs in 100k range, brick if possible, in upcoming B or A areas.

Be sure to determine that each one  has a unique APN, otherwise you have multiple facilities on one plot and you will have fun with the zoning and trying to separate them into sellable properties.