Our J-130 & J-20 Jet Engines are considerably different than the other Jet Engines United Nuclear deals with.
First of all, they have no moving parts. There is nothing to wear out, and there is no complicated support equipment such as fuel & oil pumps or radiators found on turbine engines, or reed valves that wear out & break found on pulsejet engines.
At the present time, we do not sell completed J-20 or J-130 engines or parts, but we do sell the plans.
The plans are large 1:1 scale drawings (over 16 feet long for the J-130 and over 8 feet long for the J-20). The engines are fabricated from just sheet metal and tubing.  If you are good at with metalworking & fabrication (cutting, welding, forming) you can build this engine. The plans can simply be placed on top of your sheet metal and the parts cut right out.
It is a great metal shop project for the more advanced hobbyist.
The original engine & designs were produced by a close friend of Bob Lazar's, Eugene Gulhareff. Until his death, Eugene built & sold his engine for decades and met Bob in the late 1970s. Bob occasionally worked with Eugene building engines and also sold plans with some minor modifications he incorporated for Go-Kart & small vehicle use at car shows and race events.
These plans incorporate the performance changes Bob made back then and the engines actually put out about 15% more thrust than advertised. 
The engines are controlled by a simple ball valve regulating propane flow to the engine which allows them to throttle from idle (essentially zero thrust) to 100%. The engine does get red hot during operation so it cannot be built into an enclosed area unless copious amounts of ventilation are provided.


J-130 on a Go-Kart
See the youTube video:
Here


Bob in 1979 with a J-20 on his bicycle

J-20 Jet Engine Plans: $19.00