Multiply these numbers times 5 for a 20-unit. 

Tip: Take your repair estimate, multiply it by 1.2.

This is simple to achieve if you put $50,000 down on a house or multi-unit property if you purchase a property that is either  under-priced, or you purchase a 4-plex or more units where the landlord did not make repairs so he could increase the rents and you make a fer minor repairs, increase the rent and now your multi-unit property is worth $100,000 or $200,000 more than you paid and the increased value is based on both the additional income and based on the increased property value based on the rent annual Gross Income multiplied times the Gross Multiplier plus the Annual Gross Income as shown in the image below.

I use Gross Rent Multipliers to narrow down my deals.

Yes there is always a couple of HVAC units, a roof or a bathroom floor that needs replacing every year, but I have plenty of cash reserves for those things and have plenty of rent coming in every month to absorb these things with no issues.So if I have a property that rents for 1k I can just multiply by 10 to get a ball park of what that property can generate if there are no major repairs that year on that property.I actually look for things to spend money on each year so that I maintain my portfolio of properties. 

So, in Compton, the Gross Multiplier for a 4-unit property in this hot market is no less than 15.So, suppose you purchase a 4-unit property in Compton and each unit rents for $1800 per month.Your annual income will be $1800 x 4 units x 12 months = $86,400 Annual Gross Income.If the Gross Multiplier for that building is 15, then the purchase price for that building is $1,296,000The following graph shows how much profit you can earn by increasing the rents $50 when you close escrow and only $40 per month every year.

I would try and find some similar properties for sale yourself to get an idea of what kind of cap rate or rent multiplier those types of properties trade at.

The multiplier varies by industry and can be adjusted up or down based on the competitive landscape, condition of the assets and long term potential for the business.  

@Christopher LawrenceUsing permanent life insurance cash value for real estate investing is a great multiplier of wealth.

what ever you think the ARV will be multiply that by .75.