I would second those and recommend Fuji, too. They have a Nevada 6.0 that might be a choice. It will be difficult to get disc brakes at $300, I'm not familiar with pounds to dollars and bike price differences. Dual suspension bikes start around $1800. But if 300 pounds is around 500-600 USD, then you could get a pretty decent mountain bike for that amount with front suspension and disc brakes, like the Wahoo or Marlin from Trek, or a Nevada series from Fuji. For like trails that are paved 28mm stanchions will be fine, but if you ever do other off road trails, you may want 30mm or 32mm. I just put a down payment on a mountain bike and went with the bike that had the "best" fork out of the bikes I was looking at. It cost more, but that means less I'll want to upgrade later. You may want to consider a lockout feature on the front fork too, which is good for climbing hills.

Good Luck and welcome to the forum!