It is illegal, and has been for some time, for hospitals to get their formula for nothing. They have to pay for it at a commercial rate, though the manufacturers in the UK at least would probably very much like to give them it free, in exchange for an exclusive deal. This was the case years ago.
It's not really to protect breastfeeding that this law was instigated (it's late and I can't check for sure on this) but my understanding was that this was a European directive, to ensure no manufacturer could begin a cartel, and exclude other competitors, and to give a level European playing field.
Most hospitals seem to offer 3 mainstream formulas, based on what they think mothers will be able to obtain locally. They're usually Cow&Gate, SMA, and Aptamil, though Aptamil seems to be much less widely used in hospitals.
There is no reason to choose one brand over another. They are all slightly different, but we don't know if this makes much difference. The prebiotics thing has been looked at by Cochrane (independent research and finable on the web) and the concluision was that the claims for them are unjustified.
Buy the brand you can easily get at your late night corner shop, or choose the one with the prettiest tin. There are no other reasons to select one more than the other!