If you want to start out with 2, I'd say start with 2 females, but be prepared with 2 enclosures "just in case" they don't get along, as sometimes females will fight. You should also have separate enclosures to quarantine them in for a couple of months anyway after you get them; even if they come from the same source, it's helpful to make sure they're both eatin' and poopin'.
Males have been known to be successfully kept together in some instances, but I wouldn't chance it if you are a beginner. Some say males won't fight each other unless there's a female present, buuut I've read a lot more people saying it's smarter to keep males separated.
Cresties are ridiculously easy to breed, and I would not recommend housing a male with a female unless you're prepared (and the female is prepared - you don't want her to be too young or to not have enough calcium reserves). Cooling them without separating _can_ work sometimes, but again, if you are a beginner, I wouldn't recommend it, as sometimes you'll get a female that keeps on spitting out eggs despite temps.
Price range is all over, from $25 on up to $400 or more. It depends on what colors you like, how in-demand the breeder's stock is, etc. Females will almost always cost more than males. Juvies/unsexed are generally cheaper than either.
Paper towel is a decent substrate for a beginner - little risk of impaction. If you want more naturalistic, a layer of clay hydroponics balls under a layer of screen under layers of organic sphagnum peat etc. can work fine. Coir/coco fiber substrate can stain eggs and there is one source that says eggs laid in the coir can be damaged, so I tend to avoid it. Chunks of bark substrate that are small enough to get into their mouths shouldn't be used. They're really clumsy hunters and even if you don't feed live food inside their main enclosures, they might mistake a shadow for live food and take a face-dive into bark, and try to eat it.
Repashy's Crested Gecko Diet/Superfoods have worked out great for mine for the last two years. They especially love the 2-part meal some sellers have... mine go nuts for rose, fig, and papaya flavors. I have enough geckos to warrant keeping a tub of dubia roaches but if you only have 2 geckos, that would probably be overkill unless you have something else that could eat 'em. It's a lot cheaper than buying crickets every couple weeks though.
You can also feed them organic blended non-citrus fruit - again, papayas are a big hit with mine, or papaya blended with apricots, a little banana, strawberry, mango... I only feed that as a treat once every two weeks though.
Uhhh. That's a lot of words about geckos.
Here's a link to one of my fave pics from this year.
