Re: *scratching head*
The numbers seem about right. The higher you go the more fuel you will need for return though so you do have to spend more on that but it is no problem as it is not the main cost factor. There will have to be multiple burns on descent to keep the thing relatively cool and possibly stable but should not be too many. In theory you could haul ass down an then do a crazy -x*g burn just before touch down but you would need an engine that produces huge trust on demand, not an optimal solution as u use the same engine to go up.
Keep in mind that this is all just a beginning, mostly touch down tests that have been done many times before, relatively proven stuff. Once you start dealing with the low orbit re-entry, the flip in the atmosphere, things will get rough and lot of unpredictable events can happen. The success I believe largely depends on the proper timing and very good control systems. Structural dynamics will also play important role because some of the maneuvers at such high speed will create huge amounts of stress on some parts.
It is a good start though, that is for sure. Keep it up.