I personally would not buy a 306 (or a 206 or a 319) because it takes a 206 x 13 needle and those are only available in two sizes. You can find new old stock in more sizes, but they'll probably be very expensive if you do.
I have almost 30 sewing machines and they all take the same needle except my one industrial machine. (and it takes needles that are easy to find in a large size range)
Some people claim that you can time them to accept the standard needle but other people who actually know what they're doing can give you several good reasons for not attempting this little modification.
I've seen some 306's and 319's in my area and the 319's are interesting machines - but I pass on them because of the needle issue. :)