Really, these printers use a spray to replace the laser in a SLS printer. Selective laser sintering does the same thing, but uses powdered metal and a high powered laser to fuse it together. It's often used for the medical industry and produces very strong, high quality parts. It's even being used now to make parts for spacecraft.
If you want to see an awesome high/low tech approach, here's a solar powered computer using a fresnel lens and sand in the desert to fuse glass in a sort of Selective Sun Sintering: http://www.markuskayser.com/work/solarsinter/
The cheapest SLS printer I know of uses resin and is made by Norge, supposed to be released later this year. The mini version (The Ice1) is supposed to be around $13,000 I think. We'll have to see when it's released.
SD3 w/ RUMBA (8825s), merlin hot end (in pieces). Ender3 w/ silent board for PLA printing. Ender5 w/ silent board, e3d v6, new z lead screw, and glass bed. DiY Kossel w/ smoothieboard (in pieces). Vellman Vertex (in pieces)
Shapeoko2 router in process of being converted to laser engraver (in pieces)
Multicam 5000 series CNC Router w/ 11HP spindle, 5x10' table, and auto tool changer (in pieces)