The cheapest quality host is a Solarforce L2 for about $12. It's a Chinese clone of the Surefire 6P but bored for a single 18650 or two 18350's. Two RCR123/CR123's fit too but rattle a bit so a piece of rolled up paper helps cut down on the noise. They also have a single short body available for a couple bucks that lets you run a single CR123/RCR123/18350.
If you prefer AA's a good host is the Dereelight Javelin. It takes two AA's or three cells with an extender. Also Chinese but very high quality and uses the p60 engine. They have other models like the DBS that take the p60 pill (no reflector) so you can update/replace as you see fit.
I've spent a bunch of money on p60 Lego parts (relatively). Fivemega, Ronac, Oveready mainly. I think Gene Malkoff makes a host as do a few others. Surefire was obviously the first on the scene and their venerable 6p is USA made and high quality, although they won't accept a 18650 without boring. They are some of the better makers while the Chinese produced ones are far from rubbish. Think of it as the Tenacious to the Para2.
You can build your own D26/P60 dropins or buy them. As completed units they start cheap in various voltage ranges (if you want to run one cell to four) $8-20. Custom ones are about $40-50 and Tri-emitter fancy ones can get up to about $120.
I have a Solarforce M3 head in route which is basically a turbo head with a larger reflector for more throw. The LED pill is replaceable. They (and others) have even larger reflectors available. In stock trim with a larger LED, like a Cree XM-L2, a P60 is fairly floody. A pretty shallow and small (26mm) reflector can only focus so much. Smaller LED's like the XPG2 or XRE2 can toss light a very long ways even in this small reflector albeit at less overall output (ie lumens).
The DIY or semi-DIY path is pretty fun
. With a single CR123, cheap host, and nice drop in you have a very durable light with 1-4 modes and a bunch of possible accessories. If the lens, LED, or switch fail you can just replace them. Not bad for about $60 to start.
I have a bunch of Peak Led Solutions smaller lights too, also made in the USA. The heads swap between similar bodies so if tech radicially changes you can buy these individually rather than seeking out someone to mod the light. They are available with variable or single mode brightness and a plethora of configurations. That...is another confusing post all together