I guess if it is important for them to be related is different for everybody.. it may not be of great concern to some. For us personally, it is really important that all our children share the same donor. For start, we dont want to be mothers who have children to multiple fathers.. we'd like our children to have the possibility of sharing the same traits/ looks etc. Plus we think it bonds us together a little more considering we will both be tummy mummies also, that the children are all related biologically.
I know blood doesn't mean family and families are made up of many different situations etc, but for us it is what we wanted!
We specifically looked for a donor who would be willing to donate now as well as in the future for more children between both my partner and I. We were lucky to find a donor which suited us and also lives interstate and is not interested in being involved in bubs life etc.. but will be known to the child in the future if the child chooses.
There are many options available but Im not sure how it works with storing for the future etc. Depends what sort of donor you are after, known, unknown. Cheapest and easiest way I'd say is with a known donor who is willing to donate in the future also, like what we are doing. Good luck!!