Even if you had blueprints that said "here's exactly how to build a space telescope" just building it and going through all the proper testing would be quite expensive. Certainly you could just privately fund, say, Johns Hopkins University's APL to build a spacecraft for you, but it would still cost hundreds of millions of dollars and still be a comparatively risky endeavor. More so when you consider that the operations side would run to the millions of dollars a month level, and require a substantial build out of infrastructure.
That sort of thing will happen, but it'll probably take until after launch costs have dropped a fair bit.
I'm not sure which Mars landers you're referring to, I'm not aware of any that were so cheap. The Mars Science Laboratory (Curiosity rover) cost $2.5 billion. The total cost of the MER rovers (Spirit and Opportunity) was $820 million. The Mars Phoenix mission cost $420 million. The Mars Pathfinder mission cost $280 million in 1996 dollars, or $380 million adjusted for inflation. There have been no other successful Mars landers within the last 2 decades.
> Even if you had blueprints that said "here's exactly how to build a space telescope" just building it and going through all the proper testing would be quite expensive.
As launch costs go down, the cost of experimentation is going to go down, leading to faster turnaround and less on-the-ground testing. Rapid iteration will eventually be the norm.
Also, the Mars landers cost $250M, well within the budget of a billionare investor.