Where can I find some?  I want a nice all original if possible.  Saw one at the local gun shop with a side folding stock for $700, is that too high?

There was a company called Mil-Tech who was refurbishing carbines,Garands,and Springfield 03-A3's to as issued condition.

They were advertising in shotgun news for some time.I couldn't find an ad for them in a recent issue so I don't know if they're still selling these.

An all original would be hard to find but not impossible.If you find 1 that's mostly all original it may be a good winter time project to restore yourself.HTH

Riverbank Armory

Fulton Armory

Miltech

Finding an "original" M1 Carbine is darn near impossible 'cuz the government reworked literally all of them between WW2 and Korea.  Bayonet lug is an immediate tip off it's not original WW2.

It's possible to reastore a M1 Carbing to original condition, but that's not original it's restored.

Side folding paratrooper stock on a $700 M1 Carbine is going to be a reproduction.

Start with a rifle with a matching barrel and receiver.  You can rework all the other parts including pulling the bayonet lug.  Can get pricy.

-- Chuck

What should I be looking for if I decide to buy one at the next gun show?

Carbine market has gotten awfully pricey in the last couple of years.

Things to look for:  Import stamp, typically on the barrel.  Collectors look down on these but if you just want a shooter it may be an option.  If has bayonet lug and/or adjustable rear sights almost certainly a rebuild.  All original carbines quite scarce, usually expensive, and many times not original but restored to original. Most parts will be stamped with builders code of somekind, but with twelve major contractors and hundreds of subcontractors a complete list of them would number in the hundreds.  Not all builders made their own barrels so mismatched barrel and receiver may still be original.  Also note there was a lot of parts swapping among the contractors.  Gun could be a mixmaster AND as it left the factory.  Rememember to buy the gun and not the story.  If the dealer says this carbine parachuted into Normandy, walk away.  99% of those stories are BS.

Some of the commercial carbines are decent but most aren't.  Best avoid them.  The Fulton, etc guns are certainly nice looking but very expensive and are basically a commercial rebuild (ie no collector value).  

For a decent non import USGI expect prices to start around $600 and escalate, at least in these parts (Iowa).  A legit paratrooper (most are fakes) could well top $1,500.  

Lots of variations in carbines.  A tricky market for the beginner.  Go slow, shop around.