I get the impression that good quality foster homes are a legend
I think it is easy to get that impression because the media reports far more about troubled foster home situations than about the successful stories. And the reality is that there are some kids who do get shuffled between various foster homes--which also gives the impression that the problem is with the foster home when very often the issue is the behavioral issues of the child. Up to 60% of the kids in foster care have some level of prenatal drug and alcohol exposure. Those exposures, coupled with the neglect, trauma and potential abuse which resulted in the child needing foster care---mean that foster kids can present with some exceptionally challenging behaviors.
So no, fostering is not a good way to "experiment" with the experience of parenting. And while MD does cover IVF, I do not think that it covers elective IVF for the purpose of single parenthood vs. infertility after a certain period of trying to get pregnant the traditional way. Or at least my MD insurance didn't six years ago when we were trying IVF.