SpaceX could drive launch costs to low earth orbit below $1000 per pound this year and down to $10 per pound by 2025

The Falcon 9 can get as cheap as $1233 per pound to low earth orbit. The Falcon Heavy could reach $750 per pound to launch to LEO. The Raptor prototype upper-stage engine is an engine being developed by SpaceX for a US Air Force contract.
The upper-stage prototype is to utilize the full-flow staged combustion engine cycle and same methalox propellants of the Raptor rocket engine that SpaceX has been developing since at least 2009. 
In January 2016, the US Air Force (USAF) awarded a US$33.6 million development contract to SpaceX to develop a prototype version of its methane-fueled reusable Raptor engine for use on the upper stage of the Falcon 9 and Falcon Heavy launch vehicles. The contract requires double-matching funding by SpaceX of at least US$67.3 million. The prototype is expected to complete testing in 2018.
Raptor is the first member of a family of cryogenic methane-fueled rocket engines under development by SpaceX. It is specifically intended to power high-performance lower and upper stages for SpaceX super-heavy launch vehicles. The engine will be powered by liquid methane and liquid oxygen (LOX), rather than the RP-1 kerosene and LOX used in all previous Falcon 9 rockets, which use Merlin 1C and 1D engines. Earlier concepts for Raptor would have used liquid hydrogen (LH2) fuel rather than methane.
The Raptor engine will have several times the thrust of the Merlin 1D vacuum engine that powers the second stage of the current Falcon 9, the Falcon 9 Full Thrust.
The broader Raptor concept "is a highly reusable methane staged-combustion engine that will power the next generation of SpaceX launch vehicles designed for the exploration and colonization of Mars". According to Elon Musk, this design will be able to achieve full reusability (all rocket stages) and, as a result, "a two order of magnitude reduction in the cost of spaceflight.
3D printing of rocket parts could enable engine designs with simpler designs and few parts. This could ultimately contribute to reducing launch costs by 50%. The reuse of the first rocket stage could reduce costs by about 40% initially. Full reusability of all rocket stages could reduce launch costs by 100 times.