Well, let's see:
Numerous sources (likely the least biased is from PBS,
http://www.pbs.org/wgbh/pages/frontline/shows/warriors/faqs/). It states that PMC's, like Blackwater (who seem to be the ones everyone thinks of -- there are other Companies, of course). That states average pay per day of $400 - $600. Granted, that's for dangerous conditions (Iraq) and they have little competition. So lets reduce that by 75%, to account for being in a more "lax" environment, and likely competition as more PMCs spring up.
Protection -- $100 per guard, per day (so their yearly salaries would be a hair over 36k). Note that includes me paying for their food and housing on my complex. 10 guards is a good number (depending on the size of the estate) but lets knock that down for a single family home, and say 2 guards (Day shift and night shift). 72k/year
I really can't find all that much information on road systems (cost of building them, anyway). However, I think the price for a yearly subscription would likely be around $1500 (only slightly higher than the average cell phone bill). This would probably be higher, since roads degrade far faster than cell towers, and require much more initial investment.
The average cost of private schooling was, in 2000 (according to the US dept. of Education) $3217/child. Counting out schooling that charged over $5000 for tuition (the "rich kid" schools) that figure drops to around $2500 -- which is, from my experience, the low end. Assuming 2 kids, you're at 5k a year. *Might* be lower with more competition.
So we're looking at right around 80k a year in expenses, NOT COUNTING paying for a conflict-settlement company (court replacement), research of your choice, charities of your choice, etc.
Even if you're in the upper middle class level (2 high paying degrees in the household, let's say Computer Science and Chemical engineering) you're looking at a combined income of probably 180 -- 200k/year. 80k is around 40% of that. Federal income tax bracket on that is 33%. I live in Tennessee, and don't pay a state income tax -- I do pay 10% sales though, so if I spend half of my money (70k, after tax) on stuff, there's another 7k to taxes. So that means I'm paying, in taxes, 66k from the income, 7k from sales, and we'll go ahead and tag another 7k for the extra gas taxes etc.
So we're about even, right? As long as I don't want a court system, and am fine with only 2 people protecting my stuff (There is the possibility, of course, of "going in on" it with your neighbors, or purchasing a house in a gated community). For that same money, the US gives me the protection of the most powerful military in the world, a fantastic, interconnected road system, pretty good schools, clean water, and some other "bonuses" (research grants and the like).
And something else to remember: guards aren't going to want less just because you make less money. Same with the road subscription, schools...so if you only make 100k, that 80k a year becomes a lot more.
Dunno -- I lowballed where I could, if you have more prescient stats please post them -- I identify as Libertarian, usually, and would love to be proven wrong on this, but the US government does a very good job of providing "bang for you buck."