Hi everybody, I need some advice.

I want to use a bike for recreation. Some will be normal family / bike path riding.

Something else I want to do is use a bike for hiking... to get from trailhead to trailhead... let me explain.
I drive anywhere from 25 minutes to an hour and a half to get to the trails in western MA (The Appalachian Trail included).

Since I hike alone often, I can only hike maybe four miles, turn around, hike back to my car and drive home. However with a bike, I could drop the bike at an end point maybe six or eight miles away, drive to the trailhead, and bike back on the roads to my car when the hike is over.

I would pretty much double my hiking mileage and views. Sometimes backtracking on a hike is OK, but sometimes I want to cover more ground.

Now here's the thing about security. Some trailheads are in populated areas, some are on old dirt roads. I would need to lock the bike up in towns / populated areas, and I am tempted to "stash" the bike in the woods near those old dirt roads.

Crazy?

To sum up with 3 questions:

1. What price range is realistic for what I want? (I should mention I really can't spend over $600--, and since I'm new (and worried about security) I would like to spend only about $300 - $400 if possible. Heck maybe what I really need is a department store cheapo?
1. What kind of bike? I'm thinking hybrid, but maybe you know better. I'm 6ft and 200 lean lbs and in good shape for a 42 year old-- I run, lift, hike, backpack, etc.
2. What kind of lock?

I'm really looking forward to adding cycling to my exercise regimen.

I'd buy a used mountain bike off of Craigslist for the type of riding you're planning to do. Craigslist is full of people trying to rip others off. Buy carefully. I recommend a bike without suspension for reliability.

Remember, most of my biking would be done on roads; only a few would be dirt roads.

you can look at craigslist if you like; check your local bike shop (LBS) for a used/markdown hardtail in your preferred price range.

RUN AWAY from dept. store cheapo's!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you want to have a good decent MTB you'll have for a long time, look in the $800-$1000 range. Seriously. With $400'ish you'll mostly be getting

a) good used if you're lucky
b) new crappy

Save a bit more.