@Mark Moore , some of your numbers don't add (or multiply) up.--$875/month is $10,500/yr not $10,800--those maintenance and management expenses seem very low.  

The 2% Rule is the same thing as using the 50% Rule and applying a 12% Cap Rate on the annual NOI.I was looking at some properties and noticed I got the same value using the 2% rule and using the 50% for an estimate of NOI and happened to be using a 12% Cap.Being a math dork I did write it out symbolically and they both reduce to the same mathematical equation (Which BTW is just multiply the monthly rent by 50).

#6 Always multiply your fair market value by either .65, .70, or .80 to get a reasonable deal for yourself or to pass along to another real estate investor!!!!

It's a force multiplier for building capital reserves to really get started on the right foot.

However, if you're trying to scale, I think @Derek Jones is correct, sell and multiply!

Then, multiply and divide by the 70% and subtract how much the repairs will cost? 

Now you need to look at the benifit of filling the pads...Lot rent is $150 per month... so some quick math...150 (per month) x 12 (months) = your gross income- $1,8001,800 (gross) x .7 (rough multiplier to figure net) = NOI / PAD @ $150 / month - $1,2601,260 (NOI) / (divided by) .11 (CAP RATE) = $11,454 Which is the value of each pad if priced at a 11 CAP-please do not try to tell me your in a 7 or 8 CAP market...

I am interested in getting an approximate value multiplier.

If you're looking for the best multiplier of the funds you have in the paid-for house, purchasing two or three other units would make the most sense.

For a high super-conservative estimate go square footage times ceiling height divided by 27(to convert cubic feet to cubic yards) thats the max amount of dumpster you  could need, then try to estimate the amount of many hours it will take multiplied by the labor rate you are comfortable with.