@Kyle McCorkel You could do it two ways:
1. Comp against other 2-4 units on a per-unit basis and adjust for differences. Most likely this is what an appraiser will do but it is less accurate.
2. Compare the NOI and cap rates against other small apartment buildings in the area (income approach). This is the way it is done for larger buildings and the way and investor would usually look at it.
The way I personally do it is to run an as-is analysis in Excel, then copy the tab and adjust figures to create one or more projected analyses (typically optimistic, pessimistic and middle). In your case a raise from $550 to $800 for $7.5k per unit is such an easy win that even your pessimistic numbers will look good.
If you have the $30k available to you, you can just take regular 1-4 unit residential financing as the units should appraise out as-is. If you need to roll the rehab into the mortgage, you will have to look for portfolio/commercial financing, or a 203k if you are going to live there.