BOSTON (TheStreet) -- The best things in life are free -- but if you want to afford a nice home comfortably in some of America's costliest housing markets, you or your family had better make $150,000 a year or more.
That's how much a study by market watcher RealtyTrac estimates buying a three-bedroom home will require in the pricey U.S. counties below.
"If you want to be in the center of everything, these are the kind of markets that you want to be in," RealtyTrac's Daren Blomquist says. "There are similar alternatives that are much more affordable, but they aren't at the very 'top of the heap.'"
Blomquist says costly counties are generally part of metro areas that have booming tech or government sectors with lots of high-paying jobs.
"For a buyer, these are areas where it's likely that home prices will always be good and it'll always be easy to find a job if you have the right skill set," he says. "And if you're an investor, these are markets where you'll always find tenants if you're renting the place and always find buyers if you need to sell."
Read on to check out five U.S. counties where you'll have to earn big bucks to prudently afford even a three-bedroom house, condo or townhouse.
Counties are listed below based on how much income you'll need to cover the mortgage, insurance, taxes and maintenance on a median-priced three-bedroom using no more than 25% of gross household earnings.
RealtyTrac based its figures on median prices for three-bedroom prices sold during 2013's fourth quarter in 325 counties with publicly available pricing and rent data. (Researchers omitted counties either not covered by U.S. Housing and Urban Development rental statistics or in states where public property records don't include sale prices.)
The figures below assume you'll buy a home with 20% down and a 4.46% 30-year fixed-rate mortgage. The research also assumes that typical property owners pay 1.04% of the home's value in annual property taxes, 0.4% for maintenance and 0.35% for insurance, but deduct property taxes and mortgage interest from their income-tax liability.
Santa Clara County, Calif.
Salary to comfortably afford a three-bedroom: $149,389
When Apple, eBay and other Silicon Valley giants call your county home, you know housing there costs big bucks.
A median three-bedroom home in Santa Clara County will set you back around $653,583 and require nearly $150,000 of household income to easily afford. That's more than 50% higher that the $91,425 median household income for residents of the 1.8 million-person county, which spreads from San Francisco Bay's southern tip to the southeast.
Blomquist attributes Santa Clara's high prices to strong demand from Silicon Valley workers and people from elsewhere in the area who actually find the county less expensive than other parts of the San Francisco/Silicon Valley region.
He says the median price for a three-bedroom Santa Clara home rose 24% in 2013, "which tells me that the market is becoming the place for people who can't afford San Francisco, San Mateo or Marin."
Arlington County, Va.
Salary to comfortably afford a three-bedroom: $158,474
This 208,000-population community across the Potomac River from Washington, D.C., attracts lots of wealthy suburbanites by offering a short commute to and from downtown via the Metro.
Arlington also hosts the Pentagon, which means lots of uniformed military personnel and defense contractors call the county home.
All of that demand helped push the median Arlington three-bedroom home's price up 10% during 2013 to $693,333.
Blomquist says the only silver lining to the cloud of high home prices is that the typical Arlington household earns $100,474 a year. Still, that's less than two-thirds of what RealtyTrac estimates a family needs to comfortably afford a three-bedroom place there.
San Mateo County, Calif.
Salary to comfortably afford a three-bedroom: $170,284
High-flying Facebook has its worldwide headquarters in San Mateo County, so you might as well "unfriend" the idea of finding affordable housing there.
That's because the 718,500-population county, between San Francisco city limits and the heart of Silicon Valley, has some of America's costliest homes.
San Mateo County saw median prices for three-bedroom homes rise 13% last year to hit $745,000.
That's not surprising given that local employers include not just Facebook, but also Genentech, Oracle and other new-economy giants. The county also hosts Sand Hill Road, which is basically the Wall Street of the U.S. venture-capital industry.
But even with gigabytes of high-tech money sloshing around, the median San Mateo County family earns just $81,609 a year. That's less than half of what RealtyTrac estimates a household needs to comfortably afford a typical three-bedroom home there.
Marin County, Calif.
Salary to comfortably afford a three-bedroom: $177,922
Marin County is such a poster child for the hip-but-affluent California lifestyle that President George W. Bush once referred to "American Taliban" member John Walker Lindh (who grew up there) as "some misguided Marin County hot-tubber."
Located just north of the San Francisco line, 252,000-person Marin hosts Belvedere, Tiburon and other super-exclusive communities. Median prices for three-bedroom homes in the county rose 15% last year to reach $778,417.
Unfortunately, locals need nearly twice Marin's County's $90,535 median household income to easily afford such places. "You have to be very wealthy to buy a house in Marin County," Blomquist says.
San Francisco, Calif.
Salary to comfortably afford a three-bedroom: $228,569
If you left your heart in San Francisco, it's probably because the local home prices gave you a heart attack.
The City by the Bay has perhaps America's most-expensive housing, with median prices on three-bedroom homes rising 9% last year to a cool $1 million. Comfortably affording such a place requires more than three times the 805,000-population community's $73,012 median annual household income.
Blomquist attributes Frisco's high prices to the booming local economy, which creates strong housing demand in a city with little buildable land because it's surrounded by water on three sides.
"San Francisco is just the epitome of a market with a very-limited housing supply and it's going to be that way forever because there's a limited amount of land," he says.