Even if the serial number is lower, Mossberg will send you the spare firing pins for free and the fix is a 20 minute job...
A guy in my dog club just had his break again, after fixing the pins already. I'm not sure if he got the "new, improved" version when he fixed it the first time, though. I would still not trust the things if you want it for range and hunting use (meaning relatively high-volume shooting).
Probably the best deal in a truly high-quality, long-lasting shotgun is an SKB. However, I believe they use a 20 Gauge frame. If that doesn't bother you, my 20 works great for hunting and what little skeet I've tried with it; the 28 feels the same. It's a bit over $900, but it's not outrageous. A friend who knows his guns (and his gunsmithing) has four of them. He's not a penny-pincher, and he shoots some valuable classics. He just knows the SKB is a really good shotgun. Used, if you can find one in 28, you should be able to get one within your budget.
Or just save your money and get a Beretta. The frame is scaled to 28, and it's a "forever gun." Eventually, it seems a lot of people end up with one anyway, whatever they started with.
IMHO you can get a used O/U for $900 and get a good deal -- IF you know what to look for because you can get screwed otherwise and I've been -- or you can pay a bit more for a new one and get a good gun. But a new 28 for $900 is probably not the best use of your $900. TANSTAAFL
Sure, some may tell you that Mossbergs are great, but I know far too many people who have had them break in a short time. I can only think of one guy whose Silver Reserve didn't break as of last year, and I haven't asked lately. I don't know anyone (in real life, not the 'net) who
really knows shotguns and who will buy Turkish. It's just a fact. Maybe they're wrong, but they have decades of experience and have seen far more than I. And for that matter, there was a guy here who was arguing with a few of us and saying that
his Silver Reserve was great. He came back a few months later and wrote that his, also, broke.