I realize this thread is a bit old, but I have researched that question a LOT so thought I'd add my two cents.
Most of the PM co's I talked to said 60 units was pretty much the bare minimum to bring them in, but 80 was their preferred minimum. In that range the fees were 3.75-4%. I didn't see what size property you were talking about, but 10% would be expected if you're looking at 5-40 units or so. I did talk to some of the off-site companies, that do not ever have office hours at the property, and the best I found was around 5%. The problem was the leasing fees were 50% of first months rent, plus $100 for every renewal. The management fee was offset by the lack of having to pay part-time staff. Keep in mind that avg apartment turnover can be 60%, so the fees can be huge.
For that reason I'm self-managing a 32 unit. I do have on-site leasing and maintenance people, just no management co. to do reporting, accounting, buying decisions, vendor relations, bill paying, etc. There's a post on here somewhere in which I asked for suggestions on how to manage a property that size, and I got quite varied replies. A few blasted me for even considering doing it myself. It can be done, but it will take up a lot of your time in the beginning. About five months in, the amount of time I spent on site dropped to near zero. The problem is, I've talked to many other owners doing it this way that have had nothing but problems due to their staff. That will make all the difference in the world. I got very lucky in that we have great people running the place, but I've spent a lot of time getting other options ready because I know it could change instantly.
I would keep talking to different PM's if you're looking to buy in SA. They can help you quite a bit in the buying process, and you may decide to use them in the future so you'll already have a relationship with them.
The other thing that may help you is to talk to other properties in the area and see who they're using. Almost every company I talked to was willing to manage our property for less if they already had people in the area. Its much easier for them if they can leverage staff already in place as long as the two properties are not competing. Maybe you could talk to bigger properties if you're looking at smaller ones. Or if you're looking at class C, go talk to the management co of a B class property nearby. They usually don't compete for the same tenants.