I keg and have 1 20 pound tank with double regulator and one 10 pound with single, 11 or so ball kegs and a beer gun. I don't have a tap system at home, I'll bottle or bring kegs to a party.
I've bought most of my stuff online when I see things on sale. 25-35 bucks would be good prices for used kegs shipped, having them cleaned doesn't mean much, you can use PBW or peroxide yourself. Taking them apart and changing the O rings is good practice. The poppet valves are not changed in kegs I've seen advertised as reconditioned ... so they may be of questionable state anyhow. I don't replace them all .. just have a few on hand for repairs if needed.
Shipping cost generally kills the price buying shipped kegs, but I have seen them on sale for 20-25 delivered.
I use 95% barbed fittings but have one flared for the beer gun.
I have found the green board (
www.brewboard.com) to be pretty good but I don't hang out there much (I'm EKGoldings there)
Kegging is the best thing I've ever done in homebrewing ... it makes it a heck of a lot more fun. No yeast in the beer. Beer is ready faster. I wish I started kegging 25 years ago.
You can get a cheap single stage regulator .. you really don't need to know the pressure in the tank (just the keg pressure), loss of pressure is not linear and you can weigh the thing and get a much more accurate estimate of how much is left. A 10 pound tank holds 10 pounds of CO2 and the tare weights are stamped on the tanks. Welding supply place might also e a good place to look for tanks, although they will be ugly, guaranteed. You might find better prices or better quality than what is sold in homebrew places for regulators there too. I played around with partial pressurization with nitrogen then the rest with CO2 ... definitely makes a difference, even for pale ales, but probably overkill unless you're a serious guinness fan.
Any specific questions shoot me a PM or if you're back in BB ever LMK and I'll show you my setup (and sip a few while smoking cigars of course).