Wats a really good mountain bike under 1000 dollars? It doesnt matter if its a hardtail or FS or anything.
Ok...first question. In you title you say 1000$ but in your post you say 100$. So how much. If you mean 100, I have no clue. I assume you mean 1000$ and this is a good range. What currency. Here are some bike around 1000 in cdn
1 - Kona Stuff - good freeride geometry. AWESOME frame with decent parts. Soft/plush 4 inch fork good for 90% of the xc riding involved. This is a HT.
2 - Kona Cindercone - xc geometry. Frame isn't as tough but good for a xc. Lighweight with better components than above.
3 - Norco Bigfoot - similar to the Cindercone in geometry with better overall parts.
It really depends on where and what kind of riding you plan to do. For the stuff I do a xc frame won't always cut it.
Also if you are spending american money then you can get even higher quality bikes. (damn exchange) For 1000$ american you could get an almost race quality bike in a ht.
There are many others all in different brands. Rocky Mountain is another tough bike that doesn't break the bank. Don't get a fs in this price range. The frames will always be weaker and the components will ALWAYS be lesser quality. Unless it is used, stolen or on a special sale.