Short answer is that it can vary widely depending on the neighborhood, number of units, ect... I have been studying the Twin Cities multi-family market since the start of this year and there is still way too much to learn because the Twin Cities has a lot of diverse areas. That is part of the fun of the Twin Cities.
I'm currently looking at a 4plex and a 5 unit apartment. Cap rates on those are 4-8% and I think the selling price will be somewhere between 50-70k per unit. I might be more conservative than most though when calculating cap rates.
I'm in the Detroit area and multi-family buildings, 35-45 years old, in a C area, 20-30 units cap rate is in the low 8s. That's what brokers/appraisers told me recently.
I'm looking outside the area to purchase in a good stable market with decent returns/cap rates.
In the MN market I have seen a lot of lower cap rates due to the huge growth in multi family. I office right in the area you are looking and think you can get higher cap rates in that area since it falls into a B- location vs. the low 1-3 cap rates you are seeing in class A in A locations. I think 8% is very likely, I can explain in more detail if you want to reach out. With class C properties in Brooklyn Center and Brooklyn Park market in MN we have usually averaged an increase of 10-15% ROI after doing cosmetic renovation work and simply raising rents.