i have two whites and bought them at the same time as they were already together. im not sure where to get them from in the u.s or how much but im sure if u look on forums etc and get intouch with ppl someone will b able to recommend somewhere. mine cost £15 for two (but i got them very cheap).
it can get quite pricey so try get second hand stuff. i bought my first exo terra (30x30x45cm) for £30 and that included background, canopy, jungle vine, a plant with base, two hanging plants and a bowl. i didnt need to spend much to get it complete for the frogs. just heat mat, bulb and a few other things. iv just got a new exo terra (60x45x60) with canopy and background for £50. it really does pay to look around. i did just spend another £70 on bowls, plants, bulbs etc lol. things like bulbs are goin to cost quite a bit. plus then u have all the other regular expenses of food, substrate etc. but im sure u can find some good deals. ebay and forums are a really good place to look for stuff. even if u start with the tank then buy bits each week.
i hope ur mom likes her birthday present!!