Hi,
Here's my entry to the K-Prize this SSTO ship can take at least 45t payload to 80km with a bit of practice it can get to a 80-90km orbit with around 900 oxidizer and 2000 liquid fuel for the return trip (I messed this assent up slightly so used a bit more fuel than normal but still had plenty left for return). I suppose if i used the 45t of fuel that is cargo the ship could get to even greater orbits but I am using it to construct a space station in orbit at 80km. Take off weight is 142t without a payload.
The ship includes a small service payload that I include on most trips this sits behind the small payload bay doors and includes monopropellant, batteries, large stabilizer, X200-8 tank and a large solar panel.
Costs of the ship are 142,426 without a payload and on landing you get around 130,000 back meaning to orbit and return costs are 12,000.
The ship needs to start on 4 engines due to air intake requirements but once its moving all engines can be started. This is because the ship only has 2 shock cone intakes, these provide sufficient air to power the 4 whiplash and 6 rapier engines at full throttle up to mach 4.4.
All parts are stock only plugins i use are Kerbal Engineer and Docking Port alignment indicator.
If anyone is interested in the ship file I will happily upload somewhere.