well, quite honestly if i were you, and i were looking to spend 90 dollars, i would probably buy something offline. most petstores will be in the 45-60 dollar range for cresteds.
there are several problems that are associated with the typical petstore, the main ones are as follows
you don't know the age, breeder, or previous conditions of the animal
petstores typically keep less than sanitary conditions, and will often times keep captive born animals in the same enclosures as wild caught animals, sometimes without even changing cage decorations or substrate.
they're marking the cresteds up about 200% from what they get them for or sometimes more. i sell most of my plain juvenile cresteds to pet stores for 15-25 dollars depending on how many they buy.
as far as substrate goes, i would definitely not choose anything that may be a potential choking hazard ( bark/mulch and anything rocky or gravily)
and would suggest eco earth or bed-a-beast as the top layer.
if you're going to put live plants in the cage, i personally would plant them directly in the substrate ( i use from the ground up 1-2 inches clean pea gravel, 1 inch of small clay pellets, a layer of fiberglass screen to keep the dirt from washing out, clean dirt with no fertilizer/pesticide/herbicide etc. , and finally i cover the top with eco earth)
if you want to keep it a bit simpler, as some people do, you may choose to use paper towels as the substrate, and plant the plants in pots.
however, the main thing you want to do is completely re-pot the plants being sure to remove all perlite and dirt that came in with the plant, and clean the plant leaves once or twice before putting them in the cage.
glad to see you're not buying on an impulse and doing your research. i guarentee you after you buy one, you definitely won't stop there, and would either suggest getting a plain juvenile to start off with to see how things work out, or just going for a nicer animal from the start.
cresteds are honestly one of the easiest animals to keep and breed as long as you do your research prior to getting them.
let me know if you have any more specific questions
Andrew Gilpin
L.A.C. Herps
Living Art Creations Herpetoculture
