Mountain Biking - Which bike?

I need your input. I live close to the beach (5 miles) and would like to ride on the beach, as well as around town. I am not planning on any trail riding, but I do want to be able to jump curbs and ride on gravel/sand.
Am I better off going with a mountain bike and putting on some slicker tires on it, or would a hybrid bike be a better option? No beach cruisers.
Is there a basic quality mountain bike with disc brakes that I should look for? I have about $500 to spend, so I'm guessing I'm getting a used bike.

get a pugsly and you can ride right ON the actual beach.

http://surlybikes.com/bikes/pugsley_complete/

I'd like to be able to get to and from the beach, as well. That think looks like http://4.bp.blogspot.com/_6dPn7oora60/TBahCN8XPvI/AAAAAAAAADc/vUuo-o5-aOI/s1600/JohnDeere%25255B1%25255D.jpg

Biggest semi-slicks I know of are 2.1" and are probably just OK in the sand. I'd probably stick with XC MTBs. The sand/pavement riding requires a balancing act and if you decide you want to weight your bike more towards sand riding then you'll want the fattest tires possible and many hybrids just won't take a very fat tire.

I usually only ride less than 100 yards of sand when I hit the beach - from the parking lot in a little closer to the water. If you're really gonna spend a lot of time in the sand I'd look into getting a mega fat tire bike (Surly Pugsley, Wildfire Fatbike, Salsa Mukluk, etc) but I doubt you could even get one used at your price point.

I'd like to be able to get to and from the beach, as well. That think looks like http://4.bp.blogspot.com/_6dPn7oora60/TBahCN8XPvI/AAAAAAAAADc/vUuo-o5-aOI/s1600/JohnDeere%25255B1%25255D.jpg

So fatbikes looking like tractors is a bad thing? They're the only bikes that are good in the sand, really. Even with 2.4" tires most of the time you're gonna get off your bike seconds after you leave the pavement and walk in the sand pushing your bike. I mean you CAN ride in the sand on 2.4s but it's not pleasant, it's more like a challenge to see how long you can take it.

No, it's not bad thing. I guess I was suprised to see such a fat bike. I'm a noob. I am planning on riding near the water, as much as possible, but I guess I will have to enter sand once in a while to ride around all the sprawled out sunbathers. Also, like you've mentioned, getting to the water from the parking lot, although I would like to ride the bike from home, instead of hooking it up to a car. So, I guess some asphalt riding, jumping curbs, and then wet, packed sand with some soft sand, as well.

I'd go used MTB, probably rigid. Oh, and there are some bigger semi-slicks. Schwalbe Big Apples come in a 2.35". Maxxis Hookworms in a 2.5", but they're kinda heavy.

What are some of the better rigid MTB in the $500 range? It's probably difficult to say, since many of them would be useful, but I'd appreciate any input.

What are some of the better rigid MTB in the $500 range? It's probably difficult to say, since many of them would be useful, but I'd appreciate any input.

Have you ever tried to ride a MTB in the sand? It's a beeyotch! Rider/gear weight moisture have some bearing on it. If you're a featherweight and the sand is packed/wet/tight...a 2.1-2.4" tire may be adequate, but myself...weighing 200+ lbs, riding on dry sand...it's daggum near impossible to go faster than a crawl and 1/2 the time you can't even do that.

IMO...sand riding needs the fattest tires possible.

http://www.youtube.com/watch?v=uPm7mVuTZMU