I've just bought one for my son to use, similar situation, but luckily, I know someone whom works on all the models.
Stihl seem to be the best, and I got a ms181, with a 14"bar, this is a very good entry level saw, and later will always useful as a limbing saw, possibly with a 12" bar.
Stihl, as mentioned will not allow dealers to sell a saw without going through the starting process and some safety considerations.
As I understand, the sale of a top handle saw for arborist use is illegal without the sight of a certificate to a dealer in either new, or second hand, 'though I believe some don't care.
The Arborist saw being a top handle is dangerous to use with fewer safeguards.
The best place for a good price and some safety equipment would more than likely be an agricultural dealer's. They generally sell equestrian needs and farmers gates feedstuffs etc.
You may have one near you, Though ebay listings do have new saw's for sale at a good price, and posted, which is tempting They may well buy 10, or 20, saws at a good discount, and sell them on.
Good luck with the saw buying, HTH Regards Rodders