I buy and sell a few and generally if they are an unknown name (but not Gear4music or similar) then I ask around £200 and usually accept £150+. I generally buy WITH ISSUES at £50-100 and then do a bit of work, so I think yours is a genuine bargain, especially as it’s Vietnamese not Chinese. As I said above, I have had hands on one and they are a step up from generic Chinese. It has to be worth £125 all day long but I guess Basschat is a narrow market for such things.
And there are sax forums but they are obscenely snobby and I only use them for Yamaha or better, something like yours will just get abuse. It may be worth giving the guy at The sax shack a shout, until recently he had a physical shop in Stoke but is only online now. He is a top bloke and genuine music lover, starter saxs like yours always sell well. I have sold a few through him and his reputation means that even after commission I have got more than I would have though a private sale.