I had looked at Police Surplus vests. I believe if memory serves me well they were around $150, but I don't remember the brand. They were mostly previously issued. If you can provide more insight onto this, please do. I like keeping options in the back of my mind. And putting a few Afghan veteran friends to work would be great. If you want to give me a breakdown of what to look for and what to avoid, please email me or send a PM.
You'll have trouble getting insurance if you mess around with police surplus vests. If it is something that you as an employer are going to provide, you'll want to stick to vests approved under the current NIJ standard. Velocity levels increased across the board in terms what would be stopped - partially due to the popularity of the .357 Sig and 5.7mm FN and wear resistance is now something that is tested for to a greater degree. Downside is that is now much more expensive to get vests submitted and certified and the cost is passed on to the consumer.
Warranty on a vest is generally for five years. They don't per se die at five years and day one, but they can get worn, damaged, etc. This is why any used armor is a bit of a risk. It might have sat in storage on a shelf, but it might have been worn by a big sweaty fat guy who fell in the river with it, took it home and put it through the wash and then cleaned it with gasoline later. You just never know.
The cheapest vests that I know people to wear are the Marom Dolphin ones made in Israel. They do make concealables as well as the external wear tac vests. Some Izzy stuff is junk, some is a good value. These are in the good value category. Otherwise Galls housebrand is about the cheapest of the reputable makes.
Most people that can't afford a quality U.S. set up of tac armor end up with either an Izzy vest or wearing rifle plates over a concealable.
Though you can try bulletproofme.com and muck about and it'll at least be "okay" armor that you get. They'll also sell you cheap but heavy Level III rifle plates and you can figure out a way to deal with the spalling. Steel is heavy but idiot proof. Any of the ceramic rifle plates, pay attention to the "handle with care" stamped on them. Drop them and they'll risk damage. With the "plastic" ones, don't leave them in the hot sun or the trunk of a hot car all day. With steel... kick it, drop it, drag it around... it's literally armor plate.
There's an emerging market for concealable and semi concealable rifle plates that are lighter weight. Down south of the border where 5.7mm in AP format turns up along with some other things that aren't commonly seen in the states, it might be an issue. Before private security work started to dry up in central asia it was also an issue there, since the locals learned to use 7.62x54R weapons with AP ammo to try to drop pesky Westerners.
The newish 5.56mm black tip stuff, it used to only show up on SAW belts but became more common as of late, presents a friendly fire hazard which is the other reason that AP rifle plates, they'll be stamped Level IV+ for multi hit capability, have become popular. It'll penetrate Level III plates. Penetration is similar to the old M2 .30-06 black tip ammo of ye old days, perhaps a bit better even.
If you to work the security business in MI of the sort you're talking, I'd suggest getting a PI's lisc. I was in the process of getting one when I chanced to meet my wife and ran off and got married instead. Just get a four year CJ degree and you can apply for it directly. Otherwise you need to work so many hours under someone. See a lawyer for incorporation and all that. Sal Gani in Lansing is useful if you don't already have one.
All those sorts of jobs, along with slumlording, are much less interesting than you'd think. Esp when you get old.
If you just want something good for yourself, look for a Point Blank IIIA with Thor's shield technology. These are the new ones that are "taser proof".
RKO, if he's still around the forum, used to deal in armor.