Can i use same press release for 10 sites?

If i write a unique press release to how many sites i can submit it?
Or should i write for every site a unique PR ? this would be cost much..
how many backlinks per PR ? 1 to money site and 1 to authority?

A unique PR for each site is not feasible but surely the best thing to do.
Link back to authority site is overrated IMHO.
My recommendation would be to never send direct link backs to your main site.
Always have some buffer site in between to safeguard your actual money site.

People definitely submit the same article to all the press release sites they can, if you're not going to link directly to your site you can do that as well, if you want to link directly submit to the top 2-3 and that's it. Anyway, usually press releases are picked up by multiple sources and re-posted, so regardless if you want to or not the same article will appear in a lot of places.

Use the same one. Really, only a couple will end up sticking so it's not a big deal.

Really don't worry about that. Press releases are mostly distributed to dozens, if not hundreds of sites, so this is really not a problem at all.